// Algorithm implementation -*- C++ -*-

// Copyright (C) 2001-2013 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/*
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1996
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */

/** @file bits/stl_algo.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{algorithm}
 */

#ifndef _STL_ALGO_H
#define _STL_ALGO_H 1

#include <cstdlib>             // for rand
#include <bits/algorithmfwd.h>
#include <bits/stl_heap.h>
#include <bits/stl_tempbuf.h>  // for _Temporary_buffer

#if __cplusplus >= 201103L
#include <random>     // for std::uniform_int_distribution
#include <functional> // for std::bind
#endif

// See concept_check.h for the __glibcxx_*_requires macros.

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /// Swaps the median value of *__a, *__b and *__c to *__a
  template<typename _Iterator>
    void
    __move_median_first(_Iterator __a, _Iterator __b, _Iterator __c)
    {
      // concept requirements
      __glibcxx_function_requires(_LessThanComparableConcept<
	    typename iterator_traits<_Iterator>::value_type>)

      if (*__a < *__b)
	{
	  if (*__b < *__c)
	    std::iter_swap(__a, __b);
	  else if (*__a < *__c)
	    std::iter_swap(__a, __c);
	}
      else if (*__a < *__c)
	return;
      else if (*__b < *__c)
	std::iter_swap(__a, __c);
      else
	std::iter_swap(__a, __b);
    }

  /// Swaps the median value of *__a, *__b and *__c under __comp to *__a
  template<typename _Iterator, typename _Compare>
    void
    __move_median_first(_Iterator __a, _Iterator __b, _Iterator __c,
			_Compare __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_BinaryFunctionConcept<_Compare, bool,
	    typename iterator_traits<_Iterator>::value_type,
	    typename iterator_traits<_Iterator>::value_type>)

      if (__comp(*__a, *__b))
	{
	  if (__comp(*__b, *__c))
	    std::iter_swap(__a, __b);
	  else if (__comp(*__a, *__c))
	    std::iter_swap(__a, __c);
	}
      else if (__comp(*__a, *__c))
	return;
      else if (__comp(*__b, *__c))
	std::iter_swap(__a, __c);
      else
	std::iter_swap(__a, __b);
    }

  // for_each

  /// This is an overload used by find() for the Input Iterator case.
  template<typename _InputIterator, typename _Tp>
    inline _InputIterator
    __find(_InputIterator __first, _InputIterator __last,
	   const _Tp& __val, input_iterator_tag)
    {
      while (__first != __last && !(*__first == __val))
	++__first;
      return __first;
    }

  /// This is an overload used by find_if() for the Input Iterator case.
  template<typename _InputIterator, typename _Predicate>
    inline _InputIterator
    __find_if(_InputIterator __first, _InputIterator __last,
	      _Predicate __pred, input_iterator_tag)
    {
      while (__first != __last && !bool(__pred(*__first)))
	++__first;
      return __first;
    }

  /// This is an overload used by find() for the RAI case.
  template<typename _RandomAccessIterator, typename _Tp>
    _RandomAccessIterator
    __find(_RandomAccessIterator __first, _RandomAccessIterator __last,
	   const _Tp& __val, random_access_iterator_tag)
    {
      typename iterator_traits<_RandomAccessIterator>::difference_type
	__trip_count = (__last - __first) >> 2;

      for (; __trip_count > 0; --__trip_count)
	{
	  if (*__first == __val)
	    return __first;
	  ++__first;

	  if (*__first == __val)
	    return __first;
	  ++__first;

	  if (*__first == __val)
	    return __first;
	  ++__first;

	  if (*__first == __val)
	    return __first;
	  ++__first;
	}

      switch (__last - __first)
	{
	case 3:
	  if (*__first == __val)
	    return __first;
	  ++__first;
	case 2:
	  if (*__first == __val)
	    return __first;
	  ++__first;
	case 1:
	  if (*__first == __val)
	    return __first;
	  ++__first;
	case 0:
	default:
	  return __last;
	}
    }

  /// This is an overload used by find_if() for the RAI case.
  template<typename _RandomAccessIterator, typename _Predicate>
    _RandomAccessIterator
    __find_if(_RandomAccessIterator __first, _RandomAccessIterator __last,
	      _Predicate __pred, random_access_iterator_tag)
    {
      typename iterator_traits<_RandomAccessIterator>::difference_type
	__trip_count = (__last - __first) >> 2;

      for (; __trip_count > 0; --__trip_count)
	{
	  if (__pred(*__first))
	    return __first;
	  ++__first;

	  if (__pred(*__first))
	    return __first;
	  ++__first;

	  if (__pred(*__first))
	    return __first;
	  ++__first;

	  if (__pred(*__first))
	    return __first;
	  ++__first;
	}

      switch (__last - __first)
	{
	case 3:
	  if (__pred(*__first))
	    return __first;
	  ++__first;
	case 2:
	  if (__pred(*__first))
	    return __first;
	  ++__first;
	case 1:
	  if (__pred(*__first))
	    return __first;
	  ++__first;
	case 0:
	default:
	  return __last;
	}
    }

  /// This is an overload used by find_if_not() for the Input Iterator case.
  template<typename _InputIterator, typename _Predicate>
    inline _InputIterator
    __find_if_not(_InputIterator __first, _InputIterator __last,
		  _Predicate __pred, input_iterator_tag)
    {
      while (__first != __last && bool(__pred(*__first)))
	++__first;
      return __first;
    }

  /// This is an overload used by find_if_not() for the RAI case.
  template<typename _RandomAccessIterator, typename _Predicate>
    _RandomAccessIterator
    __find_if_not(_RandomAccessIterator __first, _RandomAccessIterator __last,
		  _Predicate __pred, random_access_iterator_tag)
    {
      typename iterator_traits<_RandomAccessIterator>::difference_type
	__trip_count = (__last - __first) >> 2;

      for (; __trip_count > 0; --__trip_count)
	{
	  if (!bool(__pred(*__first)))
	    return __first;
	  ++__first;

	  if (!bool(__pred(*__first)))
	    return __first;
	  ++__first;

	  if (!bool(__pred(*__first)))
	    return __first;
	  ++__first;

	  if (!bool(__pred(*__first)))
	    return __first;
	  ++__first;
	}

      switch (__last - __first)
	{
	case 3:
	  if (!bool(__pred(*__first)))
	    return __first;
	  ++__first;
	case 2:
	  if (!bool(__pred(*__first)))
	    return __first;
	  ++__first;
	case 1:
	  if (!bool(__pred(*__first)))
	    return __first;
	  ++__first;
	case 0:
	default:
	  return __last;
	}
    }

  /// Provided for stable_partition to use.
  template<typename _InputIterator, typename _Predicate>
    inline _InputIterator
    __find_if_not(_InputIterator __first, _InputIterator __last,
		  _Predicate __pred)
    {
      return std::__find_if_not(__first, __last, __pred,
				std::__iterator_category(__first));
    }

  /// Like find_if_not(), but uses and updates a count of the
  /// remaining range length instead of comparing against an end
  /// iterator.
  template<typename _InputIterator, typename _Predicate, typename _Distance>
    _InputIterator
    __find_if_not_n(_InputIterator __first, _Distance& __len, _Predicate __pred)
    {
      for (; __len; --__len, ++__first)
	if (!bool(__pred(*__first)))
	  break;
      return __first;
    }

  // set_difference
  // set_intersection
  // set_symmetric_difference
  // set_union
  // for_each
  // find
  // find_if
  // find_first_of
  // adjacent_find
  // count
  // count_if
  // search

  /**
   *  This is an uglified
   *  search_n(_ForwardIterator, _ForwardIterator, _Integer, const _Tp&)
   *  overloaded for forward iterators.
  */
  template<typename _ForwardIterator, typename _Integer, typename _Tp>
    _ForwardIterator
    __search_n(_ForwardIterator __first, _ForwardIterator __last,
	       _Integer __count, const _Tp& __val,
	       std::forward_iterator_tag)
    {
      __first = _GLIBCXX_STD_A::find(__first, __last, __val);
      while (__first != __last)
	{
	  typename iterator_traits<_ForwardIterator>::difference_type
	    __n = __count;
	  _ForwardIterator __i = __first;
	  ++__i;
	  while (__i != __last && __n != 1 && *__i == __val)
	    {
	      ++__i;
	      --__n;
	    }
	  if (__n == 1)
	    return __first;
	  if (__i == __last)
	    return __last;
	  __first = _GLIBCXX_STD_A::find(++__i, __last, __val);
	}
      return __last;
    }

  /**
   *  This is an uglified
   *  search_n(_ForwardIterator, _ForwardIterator, _Integer, const _Tp&)
   *  overloaded for random access iterators.
  */
  template<typename _RandomAccessIter, typename _Integer, typename _Tp>
    _RandomAccessIter
    __search_n(_RandomAccessIter __first, _RandomAccessIter __last,
	       _Integer __count, const _Tp& __val, 
	       std::random_access_iterator_tag)
    {
      
      typedef typename std::iterator_traits<_RandomAccessIter>::difference_type
	_DistanceType;

      _DistanceType __tailSize = __last - __first;
      const _DistanceType __pattSize = __count;

      if (__tailSize < __pattSize)
        return __last;

      const _DistanceType __skipOffset = __pattSize - 1;
      _RandomAccessIter __lookAhead = __first + __skipOffset;
      __tailSize -= __pattSize;

      while (1) // the main loop...
	{
	  // __lookAhead here is always pointing to the last element of next 
	  // possible match.
	  while (!(*__lookAhead == __val)) // the skip loop...
	    {
	      if (__tailSize < __pattSize)
		return __last;  // Failure
	      __lookAhead += __pattSize;
	      __tailSize -= __pattSize;
	    }
	  _DistanceType __remainder = __skipOffset;
	  for (_RandomAccessIter __backTrack = __lookAhead - 1; 
	       *__backTrack == __val; --__backTrack)
	    {
	      if (--__remainder == 0)
		return (__lookAhead - __skipOffset); // Success
	    }
	  if (__remainder > __tailSize)
	    return __last; // Failure
	  __lookAhead += __remainder;
	  __tailSize -= __remainder;
	}
    }

  // search_n

  /**
   *  This is an uglified
   *  search_n(_ForwardIterator, _ForwardIterator, _Integer, const _Tp&,
   *	       _BinaryPredicate)
   *  overloaded for forward iterators.
  */
  template<typename _ForwardIterator, typename _Integer, typename _Tp,
           typename _BinaryPredicate>
    _ForwardIterator
    __search_n(_ForwardIterator __first, _ForwardIterator __last,
	       _Integer __count, const _Tp& __val,
	       _BinaryPredicate __binary_pred, std::forward_iterator_tag)
    {
      while (__first != __last && !bool(__binary_pred(*__first, __val)))
        ++__first;

      while (__first != __last)
	{
	  typename iterator_traits<_ForwardIterator>::difference_type
	    __n = __count;
	  _ForwardIterator __i = __first;
	  ++__i;
	  while (__i != __last && __n != 1 && bool(__binary_pred(*__i, __val)))
	    {
	      ++__i;
	      --__n;
	    }
	  if (__n == 1)
	    return __first;
	  if (__i == __last)
	    return __last;
	  __first = ++__i;
	  while (__first != __last
		 && !bool(__binary_pred(*__first, __val)))
	    ++__first;
	}
      return __last;
    }

  /**
   *  This is an uglified
   *  search_n(_ForwardIterator, _ForwardIterator, _Integer, const _Tp&,
   *	       _BinaryPredicate)
   *  overloaded for random access iterators.
  */
  template<typename _RandomAccessIter, typename _Integer, typename _Tp,
	   typename _BinaryPredicate>
    _RandomAccessIter
    __search_n(_RandomAccessIter __first, _RandomAccessIter __last,
	       _Integer __count, const _Tp& __val,
	       _BinaryPredicate __binary_pred, std::random_access_iterator_tag)
    {
      
      typedef typename std::iterator_traits<_RandomAccessIter>::difference_type
	_DistanceType;

      _DistanceType __tailSize = __last - __first;
      const _DistanceType __pattSize = __count;

      if (__tailSize < __pattSize)
        return __last;

      const _DistanceType __skipOffset = __pattSize - 1;
      _RandomAccessIter __lookAhead = __first + __skipOffset;
      __tailSize -= __pattSize;

      while (1) // the main loop...
	{
	  // __lookAhead here is always pointing to the last element of next 
	  // possible match.
	  while (!bool(__binary_pred(*__lookAhead, __val))) // the skip loop...
	    {
	      if (__tailSize < __pattSize)
		return __last;  // Failure
	      __lookAhead += __pattSize;
	      __tailSize -= __pattSize;
	    }
	  _DistanceType __remainder = __skipOffset;
	  for (_RandomAccessIter __backTrack = __lookAhead - 1; 
	       __binary_pred(*__backTrack, __val); --__backTrack)
	    {
	      if (--__remainder == 0)
		return (__lookAhead - __skipOffset); // Success
	    }
	  if (__remainder > __tailSize)
	    return __last; // Failure
	  __lookAhead += __remainder;
	  __tailSize -= __remainder;
	}
    }

  // find_end for forward iterators.
  template<typename _ForwardIterator1, typename _ForwardIterator2>
    _ForwardIterator1
    __find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
	       _ForwardIterator2 __first2, _ForwardIterator2 __last2,
	       forward_iterator_tag, forward_iterator_tag)
    {
      if (__first2 == __last2)
	return __last1;
      else
	{
	  _ForwardIterator1 __result = __last1;
	  while (1)
	    {
	      _ForwardIterator1 __new_result
		= _GLIBCXX_STD_A::search(__first1, __last1, __first2, __last2);
	      if (__new_result == __last1)
		return __result;
	      else
		{
		  __result = __new_result;
		  __first1 = __new_result;
		  ++__first1;
		}
	    }
	}
    }

  template<typename _ForwardIterator1, typename _ForwardIterator2,
	   typename _BinaryPredicate>
    _ForwardIterator1
    __find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
	       _ForwardIterator2 __first2, _ForwardIterator2 __last2,
	       forward_iterator_tag, forward_iterator_tag,
	       _BinaryPredicate __comp)
    {
      if (__first2 == __last2)
	return __last1;
      else
	{
	  _ForwardIterator1 __result = __last1;
	  while (1)
	    {
	      _ForwardIterator1 __new_result
		= _GLIBCXX_STD_A::search(__first1, __last1, __first2,
					 __last2, __comp);
	      if (__new_result == __last1)
		return __result;
	      else
		{
		  __result = __new_result;
		  __first1 = __new_result;
		  ++__first1;
		}
	    }
	}
    }

  // find_end for bidirectional iterators (much faster).
  template<typename _BidirectionalIterator1, typename _BidirectionalIterator2>
    _BidirectionalIterator1
    __find_end(_BidirectionalIterator1 __first1,
	       _BidirectionalIterator1 __last1,
	       _BidirectionalIterator2 __first2,
	       _BidirectionalIterator2 __last2,
	       bidirectional_iterator_tag, bidirectional_iterator_tag)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator1>)
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator2>)

      typedef reverse_iterator<_BidirectionalIterator1> _RevIterator1;
      typedef reverse_iterator<_BidirectionalIterator2> _RevIterator2;

      _RevIterator1 __rlast1(__first1);
      _RevIterator2 __rlast2(__first2);
      _RevIterator1 __rresult = _GLIBCXX_STD_A::search(_RevIterator1(__last1),
						       __rlast1,
						       _RevIterator2(__last2),
						       __rlast2);

      if (__rresult == __rlast1)
	return __last1;
      else
	{
	  _BidirectionalIterator1 __result = __rresult.base();
	  std::advance(__result, -std::distance(__first2, __last2));
	  return __result;
	}
    }

  template<typename _BidirectionalIterator1, typename _BidirectionalIterator2,
	   typename _BinaryPredicate>
    _BidirectionalIterator1
    __find_end(_BidirectionalIterator1 __first1,
	       _BidirectionalIterator1 __last1,
	       _BidirectionalIterator2 __first2,
	       _BidirectionalIterator2 __last2,
	       bidirectional_iterator_tag, bidirectional_iterator_tag,
	       _BinaryPredicate __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator1>)
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator2>)

      typedef reverse_iterator<_BidirectionalIterator1> _RevIterator1;
      typedef reverse_iterator<_BidirectionalIterator2> _RevIterator2;

      _RevIterator1 __rlast1(__first1);
      _RevIterator2 __rlast2(__first2);
      _RevIterator1 __rresult = std::search(_RevIterator1(__last1), __rlast1,
					    _RevIterator2(__last2), __rlast2,
					    __comp);

      if (__rresult == __rlast1)
	return __last1;
      else
	{
	  _BidirectionalIterator1 __result = __rresult.base();
	  std::advance(__result, -std::distance(__first2, __last2));
	  return __result;
	}
    }

  /**
   *  @brief  Find last matching subsequence in a sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  Start of range to search.
   *  @param  __last1   End of range to search.
   *  @param  __first2  Start of sequence to match.
   *  @param  __last2   End of sequence to match.
   *  @return   The last iterator @c i in the range
   *  @p [__first1,__last1-(__last2-__first2)) such that @c *(i+N) ==
   *  @p *(__first2+N) for each @c N in the range @p
   *  [0,__last2-__first2), or @p __last1 if no such iterator exists.
   *
   *  Searches the range @p [__first1,__last1) for a sub-sequence that
   *  compares equal value-by-value with the sequence given by @p
   *  [__first2,__last2) and returns an iterator to the __first
   *  element of the sub-sequence, or @p __last1 if the sub-sequence
   *  is not found.  The sub-sequence will be the last such
   *  subsequence contained in [__first,__last1).
   *
   *  Because the sub-sequence must lie completely within the range @p
   *  [__first1,__last1) it must start at a position less than @p
   *  __last1-(__last2-__first2) where @p __last2-__first2 is the
   *  length of the sub-sequence.  This means that the returned
   *  iterator @c i will be in the range @p
   *  [__first1,__last1-(__last2-__first2))
  */
  template<typename _ForwardIterator1, typename _ForwardIterator2>
    inline _ForwardIterator1
    find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
	     _ForwardIterator2 __first2, _ForwardIterator2 __last2)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
      __glibcxx_function_requires(_EqualOpConcept<
	    typename iterator_traits<_ForwardIterator1>::value_type,
	    typename iterator_traits<_ForwardIterator2>::value_type>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);

      return std::__find_end(__first1, __last1, __first2, __last2,
			     std::__iterator_category(__first1),
			     std::__iterator_category(__first2));
    }

  /**
   *  @brief  Find last matching subsequence in a sequence using a predicate.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  Start of range to search.
   *  @param  __last1   End of range to search.
   *  @param  __first2  Start of sequence to match.
   *  @param  __last2   End of sequence to match.
   *  @param  __comp    The predicate to use.
   *  @return The last iterator @c i in the range @p
   *  [__first1,__last1-(__last2-__first2)) such that @c
   *  predicate(*(i+N), @p (__first2+N)) is true for each @c N in the
   *  range @p [0,__last2-__first2), or @p __last1 if no such iterator
   *  exists.
   *
   *  Searches the range @p [__first1,__last1) for a sub-sequence that
   *  compares equal value-by-value with the sequence given by @p
   *  [__first2,__last2) using comp as a predicate and returns an
   *  iterator to the first element of the sub-sequence, or @p __last1
   *  if the sub-sequence is not found.  The sub-sequence will be the
   *  last such subsequence contained in [__first,__last1).
   *
   *  Because the sub-sequence must lie completely within the range @p
   *  [__first1,__last1) it must start at a position less than @p
   *  __last1-(__last2-__first2) where @p __last2-__first2 is the
   *  length of the sub-sequence.  This means that the returned
   *  iterator @c i will be in the range @p
   *  [__first1,__last1-(__last2-__first2))
  */
  template<typename _ForwardIterator1, typename _ForwardIterator2,
	   typename _BinaryPredicate>
    inline _ForwardIterator1
    find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
	     _ForwardIterator2 __first2, _ForwardIterator2 __last2,
	     _BinaryPredicate __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
	    typename iterator_traits<_ForwardIterator1>::value_type,
	    typename iterator_traits<_ForwardIterator2>::value_type>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);

      return std::__find_end(__first1, __last1, __first2, __last2,
			     std::__iterator_category(__first1),
			     std::__iterator_category(__first2),
			     __comp);
    }

#if __cplusplus >= 201103L
  /**
   *  @brief  Checks that a predicate is true for all the elements
   *          of a sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first   An input iterator.
   *  @param  __last    An input iterator.
   *  @param  __pred    A predicate.
   *  @return  True if the check is true, false otherwise.
   *
   *  Returns true if @p __pred is true for each element in the range
   *  @p [__first,__last), and false otherwise.
  */
  template<typename _InputIterator, typename _Predicate>
    inline bool
    all_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
    { return __last == std::find_if_not(__first, __last, __pred); }

  /**
   *  @brief  Checks that a predicate is false for all the elements
   *          of a sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first   An input iterator.
   *  @param  __last    An input iterator.
   *  @param  __pred    A predicate.
   *  @return  True if the check is true, false otherwise.
   *
   *  Returns true if @p __pred is false for each element in the range
   *  @p [__first,__last), and false otherwise.
  */
  template<typename _InputIterator, typename _Predicate>
    inline bool
    none_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
    { return __last == _GLIBCXX_STD_A::find_if(__first, __last, __pred); }

  /**
   *  @brief  Checks that a predicate is false for at least an element
   *          of a sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first   An input iterator.
   *  @param  __last    An input iterator.
   *  @param  __pred    A predicate.
   *  @return  True if the check is true, false otherwise.
   *
   *  Returns true if an element exists in the range @p
   *  [__first,__last) such that @p __pred is true, and false
   *  otherwise.
  */
  template<typename _InputIterator, typename _Predicate>
    inline bool
    any_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
    { return !std::none_of(__first, __last, __pred); }

  /**
   *  @brief  Find the first element in a sequence for which a
   *          predicate is false.
   *  @ingroup non_mutating_algorithms
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __pred   A predicate.
   *  @return   The first iterator @c i in the range @p [__first,__last)
   *  such that @p __pred(*i) is false, or @p __last if no such iterator exists.
  */
  template<typename _InputIterator, typename _Predicate>
    inline _InputIterator
    find_if_not(_InputIterator __first, _InputIterator __last,
		_Predicate __pred)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	      typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);
      return std::__find_if_not(__first, __last, __pred);
    }

  /**
   *  @brief  Checks whether the sequence is partitioned.
   *  @ingroup mutating_algorithms
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __pred   A predicate.
   *  @return  True if the range @p [__first,__last) is partioned by @p __pred,
   *  i.e. if all elements that satisfy @p __pred appear before those that
   *  do not.
  */
  template<typename _InputIterator, typename _Predicate>
    inline bool
    is_partitioned(_InputIterator __first, _InputIterator __last,
		   _Predicate __pred)
    {
      __first = std::find_if_not(__first, __last, __pred);
      return std::none_of(__first, __last, __pred);
    }

  /**
   *  @brief  Find the partition point of a partitioned range.
   *  @ingroup mutating_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __pred    A predicate.
   *  @return  An iterator @p mid such that @p all_of(__first, mid, __pred)
   *           and @p none_of(mid, __last, __pred) are both true.
  */
  template<typename _ForwardIterator, typename _Predicate>
    _ForwardIterator
    partition_point(_ForwardIterator __first, _ForwardIterator __last,
		    _Predicate __pred)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	      typename iterator_traits<_ForwardIterator>::value_type>)

      // A specific debug-mode test will be necessary...
      __glibcxx_requires_valid_range(__first, __last);

      typedef typename iterator_traits<_ForwardIterator>::difference_type
	_DistanceType;

      _DistanceType __len = std::distance(__first, __last);
      _DistanceType __half;
      _ForwardIterator __middle;

      while (__len > 0)
	{
	  __half = __len >> 1;
	  __middle = __first;
	  std::advance(__middle, __half);
	  if (__pred(*__middle))
	    {
	      __first = __middle;
	      ++__first;
	      __len = __len - __half - 1;
	    }
	  else
	    __len = __half;
	}
      return __first;
    }
#endif


  /**
   *  @brief Copy a sequence, removing elements of a given value.
   *  @ingroup mutating_algorithms
   *  @param  __first   An input iterator.
   *  @param  __last    An input iterator.
   *  @param  __result  An output iterator.
   *  @param  __value   The value to be removed.
   *  @return   An iterator designating the end of the resulting sequence.
   *
   *  Copies each element in the range @p [__first,__last) not equal
   *  to @p __value to the range beginning at @p __result.
   *  remove_copy() is stable, so the relative order of elements that
   *  are copied is unchanged.
  */
  template<typename _InputIterator, typename _OutputIterator, typename _Tp>
    _OutputIterator
    remove_copy(_InputIterator __first, _InputIterator __last,
		_OutputIterator __result, const _Tp& __value)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_function_requires(_EqualOpConcept<
	    typename iterator_traits<_InputIterator>::value_type, _Tp>)
      __glibcxx_requires_valid_range(__first, __last);

      for (; __first != __last; ++__first)
	if (!(*__first == __value))
	  {
	    *__result = *__first;
	    ++__result;
	  }
      return __result;
    }

  /**
   *  @brief Copy a sequence, removing elements for which a predicate is true.
   *  @ingroup mutating_algorithms
   *  @param  __first   An input iterator.
   *  @param  __last    An input iterator.
   *  @param  __result  An output iterator.
   *  @param  __pred    A predicate.
   *  @return   An iterator designating the end of the resulting sequence.
   *
   *  Copies each element in the range @p [__first,__last) for which
   *  @p __pred returns false to the range beginning at @p __result.
   *
   *  remove_copy_if() is stable, so the relative order of elements that are
   *  copied is unchanged.
  */
  template<typename _InputIterator, typename _OutputIterator,
	   typename _Predicate>
    _OutputIterator
    remove_copy_if(_InputIterator __first, _InputIterator __last,
		   _OutputIterator __result, _Predicate __pred)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      for (; __first != __last; ++__first)
	if (!bool(__pred(*__first)))
	  {
	    *__result = *__first;
	    ++__result;
	  }
      return __result;
    }

#if __cplusplus >= 201103L
  /**
   *  @brief Copy the elements of a sequence for which a predicate is true.
   *  @ingroup mutating_algorithms
   *  @param  __first   An input iterator.
   *  @param  __last    An input iterator.
   *  @param  __result  An output iterator.
   *  @param  __pred    A predicate.
   *  @return   An iterator designating the end of the resulting sequence.
   *
   *  Copies each element in the range @p [__first,__last) for which
   *  @p __pred returns true to the range beginning at @p __result.
   *
   *  copy_if() is stable, so the relative order of elements that are
   *  copied is unchanged.
  */
  template<typename _InputIterator, typename _OutputIterator,
	   typename _Predicate>
    _OutputIterator
    copy_if(_InputIterator __first, _InputIterator __last,
	    _OutputIterator __result, _Predicate __pred)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      for (; __first != __last; ++__first)
	if (__pred(*__first))
	  {
	    *__result = *__first;
	    ++__result;
	  }
      return __result;
    }


  template<typename _InputIterator, typename _Size, typename _OutputIterator>
    _OutputIterator
    __copy_n(_InputIterator __first, _Size __n,
	     _OutputIterator __result, input_iterator_tag)
    {
      if (__n > 0)
	{
	  while (true)
	    {
	      *__result = *__first;
	      ++__result;
	      if (--__n > 0)
		++__first;
	      else
		break;
	    }
	}
      return __result;
    }

  template<typename _RandomAccessIterator, typename _Size,
	   typename _OutputIterator>
    inline _OutputIterator
    __copy_n(_RandomAccessIterator __first, _Size __n,
	     _OutputIterator __result, random_access_iterator_tag)
    { return std::copy(__first, __first + __n, __result); }

  /**
   *  @brief Copies the range [first,first+n) into [result,result+n).
   *  @ingroup mutating_algorithms
   *  @param  __first  An input iterator.
   *  @param  __n      The number of elements to copy.
   *  @param  __result An output iterator.
   *  @return  result+n.
   *
   *  This inline function will boil down to a call to @c memmove whenever
   *  possible.  Failing that, if random access iterators are passed, then the
   *  loop count will be known (and therefore a candidate for compiler
   *  optimizations such as unrolling).
  */
  template<typename _InputIterator, typename _Size, typename _OutputIterator>
    inline _OutputIterator
    copy_n(_InputIterator __first, _Size __n, _OutputIterator __result)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
	    typename iterator_traits<_InputIterator>::value_type>)

      return std::__copy_n(__first, __n, __result,
			   std::__iterator_category(__first));
    }

  /**
   *  @brief Copy the elements of a sequence to separate output sequences
   *         depending on the truth value of a predicate.
   *  @ingroup mutating_algorithms
   *  @param  __first   An input iterator.
   *  @param  __last    An input iterator.
   *  @param  __out_true   An output iterator.
   *  @param  __out_false  An output iterator.
   *  @param  __pred    A predicate.
   *  @return   A pair designating the ends of the resulting sequences.
   *
   *  Copies each element in the range @p [__first,__last) for which
   *  @p __pred returns true to the range beginning at @p out_true
   *  and each element for which @p __pred returns false to @p __out_false.
  */
  template<typename _InputIterator, typename _OutputIterator1,
	   typename _OutputIterator2, typename _Predicate>
    pair<_OutputIterator1, _OutputIterator2>
    partition_copy(_InputIterator __first, _InputIterator __last,
		   _OutputIterator1 __out_true, _OutputIterator2 __out_false,
		   _Predicate __pred)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator1,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator2,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);
      
      for (; __first != __last; ++__first)
	if (__pred(*__first))
	  {
	    *__out_true = *__first;
	    ++__out_true;
	  }
	else
	  {
	    *__out_false = *__first;
	    ++__out_false;
	  }

      return pair<_OutputIterator1, _OutputIterator2>(__out_true, __out_false);
    }
#endif

  /**
   *  @brief Remove elements from a sequence.
   *  @ingroup mutating_algorithms
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __value  The value to be removed.
   *  @return   An iterator designating the end of the resulting sequence.
   *
   *  All elements equal to @p __value are removed from the range
   *  @p [__first,__last).
   *
   *  remove() is stable, so the relative order of elements that are
   *  not removed is unchanged.
   *
   *  Elements between the end of the resulting sequence and @p __last
   *  are still present, but their value is unspecified.
  */
  template<typename _ForwardIterator, typename _Tp>
    _ForwardIterator
    remove(_ForwardIterator __first, _ForwardIterator __last,
	   const _Tp& __value)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator>)
      __glibcxx_function_requires(_EqualOpConcept<
	    typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
      __glibcxx_requires_valid_range(__first, __last);

      __first = _GLIBCXX_STD_A::find(__first, __last, __value);
      if(__first == __last)
        return __first;
      _ForwardIterator __result = __first;
      ++__first;
      for(; __first != __last; ++__first)
        if(!(*__first == __value))
          {
            *__result = _GLIBCXX_MOVE(*__first);
            ++__result;
          }
      return __result;
    }

  /**
   *  @brief Remove elements from a sequence using a predicate.
   *  @ingroup mutating_algorithms
   *  @param  __first  A forward iterator.
   *  @param  __last   A forward iterator.
   *  @param  __pred   A predicate.
   *  @return   An iterator designating the end of the resulting sequence.
   *
   *  All elements for which @p __pred returns true are removed from the range
   *  @p [__first,__last).
   *
   *  remove_if() is stable, so the relative order of elements that are
   *  not removed is unchanged.
   *
   *  Elements between the end of the resulting sequence and @p __last
   *  are still present, but their value is unspecified.
  */
  template<typename _ForwardIterator, typename _Predicate>
    _ForwardIterator
    remove_if(_ForwardIterator __first, _ForwardIterator __last,
	      _Predicate __pred)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      __first = _GLIBCXX_STD_A::find_if(__first, __last, __pred);
      if(__first == __last)
        return __first;
      _ForwardIterator __result = __first;
      ++__first;
      for(; __first != __last; ++__first)
        if(!bool(__pred(*__first)))
          {
            *__result = _GLIBCXX_MOVE(*__first);
            ++__result;
          }
      return __result;
    }

  /**
   *  @brief Remove consecutive duplicate values from a sequence.
   *  @ingroup mutating_algorithms
   *  @param  __first  A forward iterator.
   *  @param  __last   A forward iterator.
   *  @return  An iterator designating the end of the resulting sequence.
   *
   *  Removes all but the first element from each group of consecutive
   *  values that compare equal.
   *  unique() is stable, so the relative order of elements that are
   *  not removed is unchanged.
   *  Elements between the end of the resulting sequence and @p __last
   *  are still present, but their value is unspecified.
  */
  template<typename _ForwardIterator>
    _ForwardIterator
    unique(_ForwardIterator __first, _ForwardIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator>)
      __glibcxx_function_requires(_EqualityComparableConcept<
		     typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      // Skip the beginning, if already unique.
      __first = _GLIBCXX_STD_A::adjacent_find(__first, __last);
      if (__first == __last)
	return __last;

      // Do the real copy work.
      _ForwardIterator __dest = __first;
      ++__first;
      while (++__first != __last)
	if (!(*__dest == *__first))
	  *++__dest = _GLIBCXX_MOVE(*__first);
      return ++__dest;
    }

  /**
   *  @brief Remove consecutive values from a sequence using a predicate.
   *  @ingroup mutating_algorithms
   *  @param  __first        A forward iterator.
   *  @param  __last         A forward iterator.
   *  @param  __binary_pred  A binary predicate.
   *  @return  An iterator designating the end of the resulting sequence.
   *
   *  Removes all but the first element from each group of consecutive
   *  values for which @p __binary_pred returns true.
   *  unique() is stable, so the relative order of elements that are
   *  not removed is unchanged.
   *  Elements between the end of the resulting sequence and @p __last
   *  are still present, but their value is unspecified.
  */
  template<typename _ForwardIterator, typename _BinaryPredicate>
    _ForwardIterator
    unique(_ForwardIterator __first, _ForwardIterator __last,
           _BinaryPredicate __binary_pred)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
		typename iterator_traits<_ForwardIterator>::value_type,
		typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      // Skip the beginning, if already unique.
      __first = _GLIBCXX_STD_A::adjacent_find(__first, __last, __binary_pred);
      if (__first == __last)
	return __last;

      // Do the real copy work.
      _ForwardIterator __dest = __first;
      ++__first;
      while (++__first != __last)
	if (!bool(__binary_pred(*__dest, *__first)))
	  *++__dest = _GLIBCXX_MOVE(*__first);
      return ++__dest;
    }

  /**
   *  This is an uglified unique_copy(_InputIterator, _InputIterator,
   *                                  _OutputIterator)
   *  overloaded for forward iterators and output iterator as result.
  */
  template<typename _ForwardIterator, typename _OutputIterator>
    _OutputIterator
    __unique_copy(_ForwardIterator __first, _ForwardIterator __last,
		  _OutputIterator __result,
		  forward_iterator_tag, output_iterator_tag)
    {
      // concept requirements -- taken care of in dispatching function
      _ForwardIterator __next = __first;
      *__result = *__first;
      while (++__next != __last)
	if (!(*__first == *__next))
	  {
	    __first = __next;
	    *++__result = *__first;
	  }
      return ++__result;
    }

  /**
   *  This is an uglified unique_copy(_InputIterator, _InputIterator,
   *                                  _OutputIterator)
   *  overloaded for input iterators and output iterator as result.
  */
  template<typename _InputIterator, typename _OutputIterator>
    _OutputIterator
    __unique_copy(_InputIterator __first, _InputIterator __last,
		  _OutputIterator __result,
		  input_iterator_tag, output_iterator_tag)
    {
      // concept requirements -- taken care of in dispatching function
      typename iterator_traits<_InputIterator>::value_type __value = *__first;
      *__result = __value;
      while (++__first != __last)
	if (!(__value == *__first))
	  {
	    __value = *__first;
	    *++__result = __value;
	  }
      return ++__result;
    }

  /**
   *  This is an uglified unique_copy(_InputIterator, _InputIterator,
   *                                  _OutputIterator)
   *  overloaded for input iterators and forward iterator as result.
  */
  template<typename _InputIterator, typename _ForwardIterator>
    _ForwardIterator
    __unique_copy(_InputIterator __first, _InputIterator __last,
		  _ForwardIterator __result,
		  input_iterator_tag, forward_iterator_tag)
    {
      // concept requirements -- taken care of in dispatching function
      *__result = *__first;
      while (++__first != __last)
	if (!(*__result == *__first))
	  *++__result = *__first;
      return ++__result;
    }

  /**
   *  This is an uglified
   *  unique_copy(_InputIterator, _InputIterator, _OutputIterator,
   *              _BinaryPredicate)
   *  overloaded for forward iterators and output iterator as result.
  */
  template<typename _ForwardIterator, typename _OutputIterator,
	   typename _BinaryPredicate>
    _OutputIterator
    __unique_copy(_ForwardIterator __first, _ForwardIterator __last,
		  _OutputIterator __result, _BinaryPredicate __binary_pred,
		  forward_iterator_tag, output_iterator_tag)
    {
      // concept requirements -- iterators already checked
      __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
	  typename iterator_traits<_ForwardIterator>::value_type,
	  typename iterator_traits<_ForwardIterator>::value_type>)

      _ForwardIterator __next = __first;
      *__result = *__first;
      while (++__next != __last)
	if (!bool(__binary_pred(*__first, *__next)))
	  {
	    __first = __next;
	    *++__result = *__first;
	  }
      return ++__result;
    }

  /**
   *  This is an uglified
   *  unique_copy(_InputIterator, _InputIterator, _OutputIterator,
   *              _BinaryPredicate)
   *  overloaded for input iterators and output iterator as result.
  */
  template<typename _InputIterator, typename _OutputIterator,
	   typename _BinaryPredicate>
    _OutputIterator
    __unique_copy(_InputIterator __first, _InputIterator __last,
		  _OutputIterator __result, _BinaryPredicate __binary_pred,
		  input_iterator_tag, output_iterator_tag)
    {
      // concept requirements -- iterators already checked
      __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
	  typename iterator_traits<_InputIterator>::value_type,
	  typename iterator_traits<_InputIterator>::value_type>)

      typename iterator_traits<_InputIterator>::value_type __value = *__first;
      *__result = __value;
      while (++__first != __last)
	if (!bool(__binary_pred(__value, *__first)))
	  {
	    __value = *__first;
	    *++__result = __value;
	  }
      return ++__result;
    }

  /**
   *  This is an uglified
   *  unique_copy(_InputIterator, _InputIterator, _OutputIterator,
   *              _BinaryPredicate)
   *  overloaded for input iterators and forward iterator as result.
  */
  template<typename _InputIterator, typename _ForwardIterator,
	   typename _BinaryPredicate>
    _ForwardIterator
    __unique_copy(_InputIterator __first, _InputIterator __last,
		  _ForwardIterator __result, _BinaryPredicate __binary_pred,
		  input_iterator_tag, forward_iterator_tag)
    {
      // concept requirements -- iterators already checked
      __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
	  typename iterator_traits<_ForwardIterator>::value_type,
	  typename iterator_traits<_InputIterator>::value_type>)

      *__result = *__first;
      while (++__first != __last)
	if (!bool(__binary_pred(*__result, *__first)))
	  *++__result = *__first;
      return ++__result;
    }

  /**
   *  This is an uglified reverse(_BidirectionalIterator,
   *                              _BidirectionalIterator)
   *  overloaded for bidirectional iterators.
  */
  template<typename _BidirectionalIterator>
    void
    __reverse(_BidirectionalIterator __first, _BidirectionalIterator __last,
	      bidirectional_iterator_tag)
    {
      while (true)
	if (__first == __last || __first == --__last)
	  return;
	else
	  {
	    std::iter_swap(__first, __last);
	    ++__first;
	  }
    }

  /**
   *  This is an uglified reverse(_BidirectionalIterator,
   *                              _BidirectionalIterator)
   *  overloaded for random access iterators.
  */
  template<typename _RandomAccessIterator>
    void
    __reverse(_RandomAccessIterator __first, _RandomAccessIterator __last,
	      random_access_iterator_tag)
    {
      if (__first == __last)
	return;
      --__last;
      while (__first < __last)
	{
	  std::iter_swap(__first, __last);
	  ++__first;
	  --__last;
	}
    }

  /**
   *  @brief Reverse a sequence.
   *  @ingroup mutating_algorithms
   *  @param  __first  A bidirectional iterator.
   *  @param  __last   A bidirectional iterator.
   *  @return   reverse() returns no value.
   *
   *  Reverses the order of the elements in the range @p [__first,__last),
   *  so that the first element becomes the last etc.
   *  For every @c i such that @p 0<=i<=(__last-__first)/2), @p reverse()
   *  swaps @p *(__first+i) and @p *(__last-(i+1))
  */
  template<typename _BidirectionalIterator>
    inline void
    reverse(_BidirectionalIterator __first, _BidirectionalIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
				  _BidirectionalIterator>)
      __glibcxx_requires_valid_range(__first, __last);
      std::__reverse(__first, __last, std::__iterator_category(__first));
    }

  /**
   *  @brief Copy a sequence, reversing its elements.
   *  @ingroup mutating_algorithms
   *  @param  __first   A bidirectional iterator.
   *  @param  __last    A bidirectional iterator.
   *  @param  __result  An output iterator.
   *  @return  An iterator designating the end of the resulting sequence.
   *
   *  Copies the elements in the range @p [__first,__last) to the
   *  range @p [__result,__result+(__last-__first)) such that the
   *  order of the elements is reversed.  For every @c i such that @p
   *  0<=i<=(__last-__first), @p reverse_copy() performs the
   *  assignment @p *(__result+(__last-__first)-1-i) = *(__first+i).
   *  The ranges @p [__first,__last) and @p
   *  [__result,__result+(__last-__first)) must not overlap.
  */
  template<typename _BidirectionalIterator, typename _OutputIterator>
    _OutputIterator
    reverse_copy(_BidirectionalIterator __first, _BidirectionalIterator __last,
		 _OutputIterator __result)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
		typename iterator_traits<_BidirectionalIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      while (__first != __last)
	{
	  --__last;
	  *__result = *__last;
	  ++__result;
	}
      return __result;
    }

  /**
   *  This is a helper function for the rotate algorithm specialized on RAIs.
   *  It returns the greatest common divisor of two integer values.
  */
  template<typename _EuclideanRingElement>
    _EuclideanRingElement
    __gcd(_EuclideanRingElement __m, _EuclideanRingElement __n)
    {
      while (__n != 0)
	{
	  _EuclideanRingElement __t = __m % __n;
	  __m = __n;
	  __n = __t;
	}
      return __m;
    }

  /// This is a helper function for the rotate algorithm.
  template<typename _ForwardIterator>
    void
    __rotate(_ForwardIterator __first,
	     _ForwardIterator __middle,
	     _ForwardIterator __last,
	     forward_iterator_tag)
    {
      if (__first == __middle || __last  == __middle)
	return;

      _ForwardIterator __first2 = __middle;
      do
	{
	  std::iter_swap(__first, __first2);
	  ++__first;
	  ++__first2;
	  if (__first == __middle)
	    __middle = __first2;
	}
      while (__first2 != __last);

      __first2 = __middle;

      while (__first2 != __last)
	{
	  std::iter_swap(__first, __first2);
	  ++__first;
	  ++__first2;
	  if (__first == __middle)
	    __middle = __first2;
	  else if (__first2 == __last)
	    __first2 = __middle;
	}
    }

   /// This is a helper function for the rotate algorithm.
  template<typename _BidirectionalIterator>
    void
    __rotate(_BidirectionalIterator __first,
	     _BidirectionalIterator __middle,
	     _BidirectionalIterator __last,
	      bidirectional_iterator_tag)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
				  _BidirectionalIterator>)

      if (__first == __middle || __last  == __middle)
	return;

      std::__reverse(__first,  __middle, bidirectional_iterator_tag());
      std::__reverse(__middle, __last,   bidirectional_iterator_tag());

      while (__first != __middle && __middle != __last)
	{
	  std::iter_swap(__first, --__last);
	  ++__first;
	}

      if (__first == __middle)
	std::__reverse(__middle, __last,   bidirectional_iterator_tag());
      else
	std::__reverse(__first,  __middle, bidirectional_iterator_tag());
    }

  /// This is a helper function for the rotate algorithm.
  template<typename _RandomAccessIterator>
    void
    __rotate(_RandomAccessIterator __first,
	     _RandomAccessIterator __middle,
	     _RandomAccessIterator __last,
	     random_access_iterator_tag)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
				  _RandomAccessIterator>)

      if (__first == __middle || __last  == __middle)
	return;

      typedef typename iterator_traits<_RandomAccessIterator>::difference_type
	_Distance;
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;

      _Distance __n = __last   - __first;
      _Distance __k = __middle - __first;

      if (__k == __n - __k)
	{
	  std::swap_ranges(__first, __middle, __middle);
	  return;
	}

      _RandomAccessIterator __p = __first;

      for (;;)
	{
	  if (__k < __n - __k)
	    {
	      if (__is_pod(_ValueType) && __k == 1)
		{
		  _ValueType __t = _GLIBCXX_MOVE(*__p);
		  _GLIBCXX_MOVE3(__p + 1, __p + __n, __p);
		  *(__p + __n - 1) = _GLIBCXX_MOVE(__t);
		  return;
		}
	      _RandomAccessIterator __q = __p + __k;
	      for (_Distance __i = 0; __i < __n - __k; ++ __i)
		{
		  std::iter_swap(__p, __q);
		  ++__p;
		  ++__q;
		}
	      __n %= __k;
	      if (__n == 0)
		return;
	      std::swap(__n, __k);
	      __k = __n - __k;
	    }
	  else
	    {
	      __k = __n - __k;
	      if (__is_pod(_ValueType) && __k == 1)
		{
		  _ValueType __t = _GLIBCXX_MOVE(*(__p + __n - 1));
		  _GLIBCXX_MOVE_BACKWARD3(__p, __p + __n - 1, __p + __n);
		  *__p = _GLIBCXX_MOVE(__t);
		  return;
		}
	      _RandomAccessIterator __q = __p + __n;
	      __p = __q - __k;
	      for (_Distance __i = 0; __i < __n - __k; ++ __i)
		{
		  --__p;
		  --__q;
		  std::iter_swap(__p, __q);
		}
	      __n %= __k;
	      if (__n == 0)
		return;
	      std::swap(__n, __k);
	    }
	}
    }

  /**
   *  @brief Rotate the elements of a sequence.
   *  @ingroup mutating_algorithms
   *  @param  __first   A forward iterator.
   *  @param  __middle  A forward iterator.
   *  @param  __last    A forward iterator.
   *  @return  Nothing.
   *
   *  Rotates the elements of the range @p [__first,__last) by 
   *  @p (__middle - __first) positions so that the element at @p __middle
   *  is moved to @p __first, the element at @p __middle+1 is moved to
   *  @p __first+1 and so on for each element in the range
   *  @p [__first,__last).
   *
   *  This effectively swaps the ranges @p [__first,__middle) and
   *  @p [__middle,__last).
   *
   *  Performs
   *   @p *(__first+(n+(__last-__middle))%(__last-__first))=*(__first+n)
   *  for each @p n in the range @p [0,__last-__first).
  */
  template<typename _ForwardIterator>
    inline void
    rotate(_ForwardIterator __first, _ForwardIterator __middle,
	   _ForwardIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator>)
      __glibcxx_requires_valid_range(__first, __middle);
      __glibcxx_requires_valid_range(__middle, __last);

      typedef typename iterator_traits<_ForwardIterator>::iterator_category
	_IterType;
      std::__rotate(__first, __middle, __last, _IterType());
    }

  /**
   *  @brief Copy a sequence, rotating its elements.
   *  @ingroup mutating_algorithms
   *  @param  __first   A forward iterator.
   *  @param  __middle  A forward iterator.
   *  @param  __last    A forward iterator.
   *  @param  __result  An output iterator.
   *  @return   An iterator designating the end of the resulting sequence.
   *
   *  Copies the elements of the range @p [__first,__last) to the
   *  range beginning at @result, rotating the copied elements by 
   *  @p (__middle-__first) positions so that the element at @p __middle
   *  is moved to @p __result, the element at @p __middle+1 is moved
   *  to @p __result+1 and so on for each element in the range @p
   *  [__first,__last).
   *
   *  Performs 
   *  @p *(__result+(n+(__last-__middle))%(__last-__first))=*(__first+n)
   *  for each @p n in the range @p [0,__last-__first).
  */
  template<typename _ForwardIterator, typename _OutputIterator>
    _OutputIterator
    rotate_copy(_ForwardIterator __first, _ForwardIterator __middle,
                _ForwardIterator __last, _OutputIterator __result)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
		typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __middle);
      __glibcxx_requires_valid_range(__middle, __last);

      return std::copy(__first, __middle,
                       std::copy(__middle, __last, __result));
    }

  /// This is a helper function...
  template<typename _ForwardIterator, typename _Predicate>
    _ForwardIterator
    __partition(_ForwardIterator __first, _ForwardIterator __last,
		_Predicate __pred, forward_iterator_tag)
    {
      if (__first == __last)
	return __first;

      while (__pred(*__first))
	if (++__first == __last)
	  return __first;

      _ForwardIterator __next = __first;

      while (++__next != __last)
	if (__pred(*__next))
	  {
	    std::iter_swap(__first, __next);
	    ++__first;
	  }

      return __first;
    }

  /// This is a helper function...
  template<typename _BidirectionalIterator, typename _Predicate>
    _BidirectionalIterator
    __partition(_BidirectionalIterator __first, _BidirectionalIterator __last,
		_Predicate __pred, bidirectional_iterator_tag)
    {
      while (true)
	{
	  while (true)
	    if (__first == __last)
	      return __first;
	    else if (__pred(*__first))
	      ++__first;
	    else
	      break;
	  --__last;
	  while (true)
	    if (__first == __last)
	      return __first;
	    else if (!bool(__pred(*__last)))
	      --__last;
	    else
	      break;
	  std::iter_swap(__first, __last);
	  ++__first;
	}
    }

  // partition

  /// This is a helper function...
  /// Requires __len != 0 and !__pred(*__first),
  /// same as __stable_partition_adaptive.
  template<typename _ForwardIterator, typename _Predicate, typename _Distance>
    _ForwardIterator
    __inplace_stable_partition(_ForwardIterator __first,
			       _Predicate __pred, _Distance __len)
    {
      if (__len == 1)
	return __first;
      _ForwardIterator __middle = __first;
      std::advance(__middle, __len / 2);
      _ForwardIterator __left_split =
	std::__inplace_stable_partition(__first, __pred, __len / 2);
      // Advance past true-predicate values to satisfy this
      // function's preconditions.
      _Distance __right_len = __len - __len / 2;
      _ForwardIterator __right_split =
	std::__find_if_not_n(__middle, __right_len, __pred);
      if (__right_len)
	__right_split = std::__inplace_stable_partition(__middle,
							__pred,
							__right_len);
      std::rotate(__left_split, __middle, __right_split);
      std::advance(__left_split, std::distance(__middle, __right_split));
      return __left_split;
    }

  /// This is a helper function...
  /// Requires __first != __last and !__pred(*__first)
  /// and __len == distance(__first, __last).
  ///
  /// !__pred(*__first) allows us to guarantee that we don't
  /// move-assign an element onto itself.
  template<typename _ForwardIterator, typename _Pointer, typename _Predicate,
	   typename _Distance>
    _ForwardIterator
    __stable_partition_adaptive(_ForwardIterator __first,
				_ForwardIterator __last,
				_Predicate __pred, _Distance __len,
				_Pointer __buffer,
				_Distance __buffer_size)
    {
      if (__len <= __buffer_size)
	{
	  _ForwardIterator __result1 = __first;
	  _Pointer __result2 = __buffer;
	  // The precondition guarantees that !__pred(*__first), so
	  // move that element to the buffer before starting the loop.
	  // This ensures that we only call __pred once per element.
	  *__result2 = _GLIBCXX_MOVE(*__first);
	  ++__result2;
	  ++__first;
	  for (; __first != __last; ++__first)
	    if (__pred(*__first))
	      {
		*__result1 = _GLIBCXX_MOVE(*__first);
		++__result1;
	      }
	    else
	      {
		*__result2 = _GLIBCXX_MOVE(*__first);
		++__result2;
	      }
	  _GLIBCXX_MOVE3(__buffer, __result2, __result1);
	  return __result1;
	}
      else
	{
	  _ForwardIterator __middle = __first;
	  std::advance(__middle, __len / 2);
	  _ForwardIterator __left_split =
	    std::__stable_partition_adaptive(__first, __middle, __pred,
					     __len / 2, __buffer,
					     __buffer_size);
	  // Advance past true-predicate values to satisfy this
	  // function's preconditions.
	  _Distance __right_len = __len - __len / 2;
	  _ForwardIterator __right_split =
	    std::__find_if_not_n(__middle, __right_len, __pred);
	  if (__right_len)
	    __right_split =
	      std::__stable_partition_adaptive(__right_split, __last, __pred,
					       __right_len,
					       __buffer, __buffer_size);
	  std::rotate(__left_split, __middle, __right_split);
	  std::advance(__left_split, std::distance(__middle, __right_split));
	  return __left_split;
	}
    }

  /**
   *  @brief Move elements for which a predicate is true to the beginning
   *         of a sequence, preserving relative ordering.
   *  @ingroup mutating_algorithms
   *  @param  __first   A forward iterator.
   *  @param  __last    A forward iterator.
   *  @param  __pred    A predicate functor.
   *  @return  An iterator @p middle such that @p __pred(i) is true for each
   *  iterator @p i in the range @p [first,middle) and false for each @p i
   *  in the range @p [middle,last).
   *
   *  Performs the same function as @p partition() with the additional
   *  guarantee that the relative ordering of elements in each group is
   *  preserved, so any two elements @p x and @p y in the range
   *  @p [__first,__last) such that @p __pred(x)==__pred(y) will have the same
   *  relative ordering after calling @p stable_partition().
  */
  template<typename _ForwardIterator, typename _Predicate>
    _ForwardIterator
    stable_partition(_ForwardIterator __first, _ForwardIterator __last,
		     _Predicate __pred)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      __first = std::__find_if_not(__first, __last, __pred);

      if (__first == __last)
	return __first;
      else
	{
	  typedef typename iterator_traits<_ForwardIterator>::value_type
	    _ValueType;
	  typedef typename iterator_traits<_ForwardIterator>::difference_type
	    _DistanceType;

	  _Temporary_buffer<_ForwardIterator, _ValueType> __buf(__first,
								__last);
	if (__buf.size() > 0)
	  return
	    std::__stable_partition_adaptive(__first, __last, __pred,
					  _DistanceType(__buf.requested_size()),
					  __buf.begin(),
					  _DistanceType(__buf.size()));
	else
	  return
	    std::__inplace_stable_partition(__first, __pred,
					 _DistanceType(__buf.requested_size()));
	}
    }

  /// This is a helper function for the sort routines.
  template<typename _RandomAccessIterator>
    void
    __heap_select(_RandomAccessIterator __first,
		  _RandomAccessIterator __middle,
		  _RandomAccessIterator __last)
    {
      std::make_heap(__first, __middle);
      for (_RandomAccessIterator __i = __middle; __i < __last; ++__i)
	if (*__i < *__first)
	  std::__pop_heap(__first, __middle, __i);
    }

  /// This is a helper function for the sort routines.
  template<typename _RandomAccessIterator, typename _Compare>
    void
    __heap_select(_RandomAccessIterator __first,
		  _RandomAccessIterator __middle,
		  _RandomAccessIterator __last, _Compare __comp)
    {
      std::make_heap(__first, __middle, __comp);
      for (_RandomAccessIterator __i = __middle; __i < __last; ++__i)
	if (__comp(*__i, *__first))
	  std::__pop_heap(__first, __middle, __i, __comp);
    }

  // partial_sort

  /**
   *  @brief Copy the smallest elements of a sequence.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __result_first   A random-access iterator.
   *  @param  __result_last    Another random-access iterator.
   *  @return   An iterator indicating the end of the resulting sequence.
   *
   *  Copies and sorts the smallest N values from the range @p [__first,__last)
   *  to the range beginning at @p __result_first, where the number of
   *  elements to be copied, @p N, is the smaller of @p (__last-__first) and
   *  @p (__result_last-__result_first).
   *  After the sort if @e i and @e j are iterators in the range
   *  @p [__result_first,__result_first+N) such that i precedes j then
   *  *j<*i is false.
   *  The value returned is @p __result_first+N.
  */
  template<typename _InputIterator, typename _RandomAccessIterator>
    _RandomAccessIterator
    partial_sort_copy(_InputIterator __first, _InputIterator __last,
		      _RandomAccessIterator __result_first,
		      _RandomAccessIterator __result_last)
    {
      typedef typename iterator_traits<_InputIterator>::value_type
	_InputValueType;
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_OutputValueType;
      typedef typename iterator_traits<_RandomAccessIterator>::difference_type
	_DistanceType;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_ConvertibleConcept<_InputValueType,
				  _OutputValueType>)
      __glibcxx_function_requires(_LessThanOpConcept<_InputValueType,
				                     _OutputValueType>)
      __glibcxx_function_requires(_LessThanComparableConcept<_OutputValueType>)
      __glibcxx_requires_valid_range(__first, __last);
      __glibcxx_requires_valid_range(__result_first, __result_last);

      if (__result_first == __result_last)
	return __result_last;
      _RandomAccessIterator __result_real_last = __result_first;
      while(__first != __last && __result_real_last != __result_last)
	{
	  *__result_real_last = *__first;
	  ++__result_real_last;
	  ++__first;
	}
      std::make_heap(__result_first, __result_real_last);
      while (__first != __last)
	{
	  if (*__first < *__result_first)
	    std::__adjust_heap(__result_first, _DistanceType(0),
			       _DistanceType(__result_real_last
					     - __result_first),
			       _InputValueType(*__first));
	  ++__first;
	}
      std::sort_heap(__result_first, __result_real_last);
      return __result_real_last;
    }

  /**
   *  @brief Copy the smallest elements of a sequence using a predicate for
   *         comparison.
   *  @ingroup sorting_algorithms
   *  @param  __first   An input iterator.
   *  @param  __last    Another input iterator.
   *  @param  __result_first   A random-access iterator.
   *  @param  __result_last    Another random-access iterator.
   *  @param  __comp    A comparison functor.
   *  @return   An iterator indicating the end of the resulting sequence.
   *
   *  Copies and sorts the smallest N values from the range @p [__first,__last)
   *  to the range beginning at @p result_first, where the number of
   *  elements to be copied, @p N, is the smaller of @p (__last-__first) and
   *  @p (__result_last-__result_first).
   *  After the sort if @e i and @e j are iterators in the range
   *  @p [__result_first,__result_first+N) such that i precedes j then
   *  @p __comp(*j,*i) is false.
   *  The value returned is @p __result_first+N.
  */
  template<typename _InputIterator, typename _RandomAccessIterator, typename _Compare>
    _RandomAccessIterator
    partial_sort_copy(_InputIterator __first, _InputIterator __last,
		      _RandomAccessIterator __result_first,
		      _RandomAccessIterator __result_last,
		      _Compare __comp)
    {
      typedef typename iterator_traits<_InputIterator>::value_type
	_InputValueType;
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_OutputValueType;
      typedef typename iterator_traits<_RandomAccessIterator>::difference_type
	_DistanceType;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
				  _RandomAccessIterator>)
      __glibcxx_function_requires(_ConvertibleConcept<_InputValueType,
				  _OutputValueType>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _InputValueType, _OutputValueType>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _OutputValueType, _OutputValueType>)
      __glibcxx_requires_valid_range(__first, __last);
      __glibcxx_requires_valid_range(__result_first, __result_last);

      if (__result_first == __result_last)
	return __result_last;
      _RandomAccessIterator __result_real_last = __result_first;
      while(__first != __last && __result_real_last != __result_last)
	{
	  *__result_real_last = *__first;
	  ++__result_real_last;
	  ++__first;
	}
      std::make_heap(__result_first, __result_real_last, __comp);
      while (__first != __last)
	{
	  if (__comp(*__first, *__result_first))
	    std::__adjust_heap(__result_first, _DistanceType(0),
			       _DistanceType(__result_real_last
					     - __result_first),
			       _InputValueType(*__first),
			       __comp);
	  ++__first;
	}
      std::sort_heap(__result_first, __result_real_last, __comp);
      return __result_real_last;
    }

  /// This is a helper function for the sort routine.
  template<typename _RandomAccessIterator>
    void
    __unguarded_linear_insert(_RandomAccessIterator __last)
    {
      typename iterator_traits<_RandomAccessIterator>::value_type
	__val = _GLIBCXX_MOVE(*__last);
      _RandomAccessIterator __next = __last;
      --__next;
      while (__val < *__next)
	{
	  *__last = _GLIBCXX_MOVE(*__next);
	  __last = __next;
	  --__next;
	}
      *__last = _GLIBCXX_MOVE(__val);
    }

  /// This is a helper function for the sort routine.
  template<typename _RandomAccessIterator, typename _Compare>
    void
    __unguarded_linear_insert(_RandomAccessIterator __last,
			      _Compare __comp)
    {
      typename iterator_traits<_RandomAccessIterator>::value_type
	__val = _GLIBCXX_MOVE(*__last);
      _RandomAccessIterator __next = __last;
      --__next;
      while (__comp(__val, *__next))
	{
	  *__last = _GLIBCXX_MOVE(*__next);
	  __last = __next;
	  --__next;
	}
      *__last = _GLIBCXX_MOVE(__val);
    }

  /// This is a helper function for the sort routine.
  template<typename _RandomAccessIterator>
    void
    __insertion_sort(_RandomAccessIterator __first,
		     _RandomAccessIterator __last)
    {
      if (__first == __last)
	return;

      for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
	{
	  if (*__i < *__first)
	    {
	      typename iterator_traits<_RandomAccessIterator>::value_type
		__val = _GLIBCXX_MOVE(*__i);
	      _GLIBCXX_MOVE_BACKWARD3(__first, __i, __i + 1);
	      *__first = _GLIBCXX_MOVE(__val);
	    }
	  else
	    std::__unguarded_linear_insert(__i);
	}
    }

  /// This is a helper function for the sort routine.
  template<typename _RandomAccessIterator, typename _Compare>
    void
    __insertion_sort(_RandomAccessIterator __first,
		     _RandomAccessIterator __last, _Compare __comp)
    {
      if (__first == __last) return;

      for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
	{
	  if (__comp(*__i, *__first))
	    {
	      typename iterator_traits<_RandomAccessIterator>::value_type
		__val = _GLIBCXX_MOVE(*__i);
	      _GLIBCXX_MOVE_BACKWARD3(__first, __i, __i + 1);
	      *__first = _GLIBCXX_MOVE(__val);
	    }
	  else
	    std::__unguarded_linear_insert(__i, __comp);
	}
    }

  /// This is a helper function for the sort routine.
  template<typename _RandomAccessIterator>
    inline void
    __unguarded_insertion_sort(_RandomAccessIterator __first,
			       _RandomAccessIterator __last)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;

      for (_RandomAccessIterator __i = __first; __i != __last; ++__i)
	std::__unguarded_linear_insert(__i);
    }

  /// This is a helper function for the sort routine.
  template<typename _RandomAccessIterator, typename _Compare>
    inline void
    __unguarded_insertion_sort(_RandomAccessIterator __first,
			       _RandomAccessIterator __last, _Compare __comp)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;

      for (_RandomAccessIterator __i = __first; __i != __last; ++__i)
	std::__unguarded_linear_insert(__i, __comp);
    }

  /**
   *  @doctodo
   *  This controls some aspect of the sort routines.
  */
  enum { _S_threshold = 16 };

  /// This is a helper function for the sort routine.
  template<typename _RandomAccessIterator>
    void
    __final_insertion_sort(_RandomAccessIterator __first,
			   _RandomAccessIterator __last)
    {
      if (__last - __first > int(_S_threshold))
	{
	  std::__insertion_sort(__first, __first + int(_S_threshold));
	  std::__unguarded_insertion_sort(__first + int(_S_threshold), __last);
	}
      else
	std::__insertion_sort(__first, __last);
    }

  /// This is a helper function for the sort routine.
  template<typename _RandomAccessIterator, typename _Compare>
    void
    __final_insertion_sort(_RandomAccessIterator __first,
			   _RandomAccessIterator __last, _Compare __comp)
    {
      if (__last - __first > int(_S_threshold))
	{
	  std::__insertion_sort(__first, __first + int(_S_threshold), __comp);
	  std::__unguarded_insertion_sort(__first + int(_S_threshold), __last,
					  __comp);
	}
      else
	std::__insertion_sort(__first, __last, __comp);
    }

  /// This is a helper function...
  template<typename _RandomAccessIterator, typename _Tp>
    _RandomAccessIterator
    __unguarded_partition(_RandomAccessIterator __first,
			  _RandomAccessIterator __last, const _Tp& __pivot)
    {
      while (true)
	{
	  while (*__first < __pivot)
	    ++__first;
	  --__last;
	  while (__pivot < *__last)
	    --__last;
	  if (!(__first < __last))
	    return __first;
	  std::iter_swap(__first, __last);
	  ++__first;
	}
    }

  /// This is a helper function...
  template<typename _RandomAccessIterator, typename _Tp, typename _Compare>
    _RandomAccessIterator
    __unguarded_partition(_RandomAccessIterator __first,
			  _RandomAccessIterator __last,
			  const _Tp& __pivot, _Compare __comp)
    {
      while (true)
	{
	  while (__comp(*__first, __pivot))
	    ++__first;
	  --__last;
	  while (__comp(__pivot, *__last))
	    --__last;
	  if (!(__first < __last))
	    return __first;
	  std::iter_swap(__first, __last);
	  ++__first;
	}
    }

  /// This is a helper function...
  template<typename _RandomAccessIterator>
    inline _RandomAccessIterator
    __unguarded_partition_pivot(_RandomAccessIterator __first,
				_RandomAccessIterator __last)
    {
      _RandomAccessIterator __mid = __first + (__last - __first) / 2;
      std::__move_median_first(__first, __mid, (__last - 1));
      return std::__unguarded_partition(__first + 1, __last, *__first);
    }


  /// This is a helper function...
  template<typename _RandomAccessIterator, typename _Compare>
    inline _RandomAccessIterator
    __unguarded_partition_pivot(_RandomAccessIterator __first,
				_RandomAccessIterator __last, _Compare __comp)
    {
      _RandomAccessIterator __mid = __first + (__last - __first) / 2;
      std::__move_median_first(__first, __mid, (__last - 1), __comp);
      return std::__unguarded_partition(__first + 1, __last, *__first, __comp);
    }

  /// This is a helper function for the sort routine.
  template<typename _RandomAccessIterator, typename _Size>
    void
    __introsort_loop(_RandomAccessIterator __first,
		     _RandomAccessIterator __last,
		     _Size __depth_limit)
    {
      while (__last - __first > int(_S_threshold))
	{
	  if (__depth_limit == 0)
	    {
	      _GLIBCXX_STD_A::partial_sort(__first, __last, __last);
	      return;
	    }
	  --__depth_limit;
	  _RandomAccessIterator __cut =
	    std::__unguarded_partition_pivot(__first, __last);
	  std::__introsort_loop(__cut, __last, __depth_limit);
	  __last = __cut;
	}
    }

  /// This is a helper function for the sort routine.
  template<typename _RandomAccessIterator, typename _Size, typename _Compare>
    void
    __introsort_loop(_RandomAccessIterator __first,
		     _RandomAccessIterator __last,
		     _Size __depth_limit, _Compare __comp)
    {
      while (__last - __first > int(_S_threshold))
	{
	  if (__depth_limit == 0)
	    {
	      _GLIBCXX_STD_A::partial_sort(__first, __last, __last, __comp);
	      return;
	    }
	  --__depth_limit;
	  _RandomAccessIterator __cut =
	    std::__unguarded_partition_pivot(__first, __last, __comp);
	  std::__introsort_loop(__cut, __last, __depth_limit, __comp);
	  __last = __cut;
	}
    }

  // sort

  template<typename _RandomAccessIterator, typename _Size>
    void
    __introselect(_RandomAccessIterator __first, _RandomAccessIterator __nth,
		  _RandomAccessIterator __last, _Size __depth_limit)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;

      while (__last - __first > 3)
	{
	  if (__depth_limit == 0)
	    {
	      std::__heap_select(__first, __nth + 1, __last);

	      // Place the nth largest element in its final position.
	      std::iter_swap(__first, __nth);
	      return;
	    }
	  --__depth_limit;
	  _RandomAccessIterator __cut =
	    std::__unguarded_partition_pivot(__first, __last);
	  if (__cut <= __nth)
	    __first = __cut;
	  else
	    __last = __cut;
	}
      std::__insertion_sort(__first, __last);
    }

  template<typename _RandomAccessIterator, typename _Size, typename _Compare>
    void
    __introselect(_RandomAccessIterator __first, _RandomAccessIterator __nth,
		  _RandomAccessIterator __last, _Size __depth_limit,
		  _Compare __comp)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;

      while (__last - __first > 3)
	{
	  if (__depth_limit == 0)
	    {
	      std::__heap_select(__first, __nth + 1, __last, __comp);
	      // Place the nth largest element in its final position.
	      std::iter_swap(__first, __nth);
	      return;
	    }
	  --__depth_limit;
	  _RandomAccessIterator __cut =
	    std::__unguarded_partition_pivot(__first, __last, __comp);
	  if (__cut <= __nth)
	    __first = __cut;
	  else
	    __last = __cut;
	}
      std::__insertion_sort(__first, __last, __comp);
    }

  // nth_element

  // lower_bound moved to stl_algobase.h

  /**
   *  @brief Finds the first position in which @p __val could be inserted
   *         without changing the ordering.
   *  @ingroup binary_search_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __val     The search term.
   *  @param  __comp    A functor to use for comparisons.
   *  @return An iterator pointing to the first element <em>not less
   *           than</em> @p __val, or end() if every element is less
   *           than @p __val.
   *  @ingroup binary_search_algorithms
   *
   *  The comparison function should have the same effects on ordering as
   *  the function used for the initial sort.
  */
  template<typename _ForwardIterator, typename _Tp, typename _Compare>
    _ForwardIterator
    lower_bound(_ForwardIterator __first, _ForwardIterator __last,
		const _Tp& __val, _Compare __comp)
    {
      typedef typename iterator_traits<_ForwardIterator>::value_type
	_ValueType;
      typedef typename iterator_traits<_ForwardIterator>::difference_type
	_DistanceType;

      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType, _Tp>)
      __glibcxx_requires_partitioned_lower_pred(__first, __last,
						__val, __comp);

      _DistanceType __len = std::distance(__first, __last);

      while (__len > 0)
	{
	  _DistanceType __half = __len >> 1;
	  _ForwardIterator __middle = __first;
	  std::advance(__middle, __half);
	  if (__comp(*__middle, __val))
	    {
	      __first = __middle;
	      ++__first;
	      __len = __len - __half - 1;
	    }
	  else
	    __len = __half;
	}
      return __first;
    }

  /**
   *  @brief Finds the last position in which @p __val could be inserted
   *         without changing the ordering.
   *  @ingroup binary_search_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __val     The search term.
   *  @return  An iterator pointing to the first element greater than @p __val,
   *           or end() if no elements are greater than @p __val.
   *  @ingroup binary_search_algorithms
  */
  template<typename _ForwardIterator, typename _Tp>
    _ForwardIterator
    upper_bound(_ForwardIterator __first, _ForwardIterator __last,
		const _Tp& __val)
    {
      typedef typename iterator_traits<_ForwardIterator>::value_type
	_ValueType;
      typedef typename iterator_traits<_ForwardIterator>::difference_type
	_DistanceType;

      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_LessThanOpConcept<_Tp, _ValueType>)
      __glibcxx_requires_partitioned_upper(__first, __last, __val);

      _DistanceType __len = std::distance(__first, __last);

      while (__len > 0)
	{
	  _DistanceType __half = __len >> 1;
	  _ForwardIterator __middle = __first;
	  std::advance(__middle, __half);
	  if (__val < *__middle)
	    __len = __half;
	  else
	    {
	      __first = __middle;
	      ++__first;
	      __len = __len - __half - 1;
	    }
	}
      return __first;
    }

  /**
   *  @brief Finds the last position in which @p __val could be inserted
   *         without changing the ordering.
   *  @ingroup binary_search_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __val     The search term.
   *  @param  __comp    A functor to use for comparisons.
   *  @return  An iterator pointing to the first element greater than @p __val,
   *           or end() if no elements are greater than @p __val.
   *  @ingroup binary_search_algorithms
   *
   *  The comparison function should have the same effects on ordering as
   *  the function used for the initial sort.
  */
  template<typename _ForwardIterator, typename _Tp, typename _Compare>
    _ForwardIterator
    upper_bound(_ForwardIterator __first, _ForwardIterator __last,
		const _Tp& __val, _Compare __comp)
    {
      typedef typename iterator_traits<_ForwardIterator>::value_type
	_ValueType;
      typedef typename iterator_traits<_ForwardIterator>::difference_type
	_DistanceType;

      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _Tp, _ValueType>)
      __glibcxx_requires_partitioned_upper_pred(__first, __last,
						__val, __comp);

      _DistanceType __len = std::distance(__first, __last);

      while (__len > 0)
	{
	  _DistanceType __half = __len >> 1;
	  _ForwardIterator __middle = __first;
	  std::advance(__middle, __half);
	  if (__comp(__val, *__middle))
	    __len = __half;
	  else
	    {
	      __first = __middle;
	      ++__first;
	      __len = __len - __half - 1;
	    }
	}
      return __first;
    }

  /**
   *  @brief Finds the largest subrange in which @p __val could be inserted
   *         at any place in it without changing the ordering.
   *  @ingroup binary_search_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __val     The search term.
   *  @return  An pair of iterators defining the subrange.
   *  @ingroup binary_search_algorithms
   *
   *  This is equivalent to
   *  @code
   *    std::make_pair(lower_bound(__first, __last, __val),
   *                   upper_bound(__first, __last, __val))
   *  @endcode
   *  but does not actually call those functions.
  */
  template<typename _ForwardIterator, typename _Tp>
    pair<_ForwardIterator, _ForwardIterator>
    equal_range(_ForwardIterator __first, _ForwardIterator __last,
		const _Tp& __val)
    {
      typedef typename iterator_traits<_ForwardIterator>::value_type
	_ValueType;
      typedef typename iterator_traits<_ForwardIterator>::difference_type
	_DistanceType;

      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType, _Tp>)
      __glibcxx_function_requires(_LessThanOpConcept<_Tp, _ValueType>)	
      __glibcxx_requires_partitioned_lower(__first, __last, __val);
      __glibcxx_requires_partitioned_upper(__first, __last, __val);      

      _DistanceType __len = std::distance(__first, __last);
 
      while (__len > 0)
	{
	  _DistanceType __half = __len >> 1;
	  _ForwardIterator __middle = __first;
	  std::advance(__middle, __half);
	  if (*__middle < __val)
	    {
	      __first = __middle;
	      ++__first;
	      __len = __len - __half - 1;
	    }
	  else if (__val < *__middle)
	    __len = __half;
	  else
	    {
	      _ForwardIterator __left = std::lower_bound(__first, __middle,
							 __val);
	      std::advance(__first, __len);
	      _ForwardIterator __right = std::upper_bound(++__middle, __first,
							  __val);
	      return pair<_ForwardIterator, _ForwardIterator>(__left, __right);
	    }
	}
      return pair<_ForwardIterator, _ForwardIterator>(__first, __first);
    }

  /**
   *  @brief Finds the largest subrange in which @p __val could be inserted
   *         at any place in it without changing the ordering.
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __val     The search term.
   *  @param  __comp    A functor to use for comparisons.
   *  @return  An pair of iterators defining the subrange.
   *  @ingroup binary_search_algorithms
   *
   *  This is equivalent to
   *  @code
   *    std::make_pair(lower_bound(__first, __last, __val, __comp),
   *                   upper_bound(__first, __last, __val, __comp))
   *  @endcode
   *  but does not actually call those functions.
  */
  template<typename _ForwardIterator, typename _Tp, typename _Compare>
    pair<_ForwardIterator, _ForwardIterator>
    equal_range(_ForwardIterator __first, _ForwardIterator __last,
		const _Tp& __val, _Compare __comp)
    {
      typedef typename iterator_traits<_ForwardIterator>::value_type
	_ValueType;
      typedef typename iterator_traits<_ForwardIterator>::difference_type
	_DistanceType;

      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType, _Tp>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _Tp, _ValueType>)
      __glibcxx_requires_partitioned_lower_pred(__first, __last,
						__val, __comp);
      __glibcxx_requires_partitioned_upper_pred(__first, __last,
						__val, __comp);

      _DistanceType __len = std::distance(__first, __last);

      while (__len > 0)
	{
	  _DistanceType __half = __len >> 1;
	  _ForwardIterator __middle = __first;
	  std::advance(__middle, __half);
	  if (__comp(*__middle, __val))
	    {
	      __first = __middle;
	      ++__first;
	      __len = __len - __half - 1;
	    }
	  else if (__comp(__val, *__middle))
	    __len = __half;
	  else
	    {
	      _ForwardIterator __left = std::lower_bound(__first, __middle,
							 __val, __comp);
	      std::advance(__first, __len);
	      _ForwardIterator __right = std::upper_bound(++__middle, __first,
							  __val, __comp);
	      return pair<_ForwardIterator, _ForwardIterator>(__left, __right);
	    }
	}
      return pair<_ForwardIterator, _ForwardIterator>(__first, __first);
    }

  /**
   *  @brief Determines whether an element exists in a range.
   *  @ingroup binary_search_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __val     The search term.
   *  @return True if @p __val (or its equivalent) is in [@p
   *  __first,@p __last ].
   *
   *  Note that this does not actually return an iterator to @p __val.  For
   *  that, use std::find or a container's specialized find member functions.
  */
  template<typename _ForwardIterator, typename _Tp>
    bool
    binary_search(_ForwardIterator __first, _ForwardIterator __last,
                  const _Tp& __val)
    {
      typedef typename iterator_traits<_ForwardIterator>::value_type
	_ValueType;

      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_LessThanOpConcept<_Tp, _ValueType>)
      __glibcxx_requires_partitioned_lower(__first, __last, __val);
      __glibcxx_requires_partitioned_upper(__first, __last, __val);

      _ForwardIterator __i = std::lower_bound(__first, __last, __val);
      return __i != __last && !(__val < *__i);
    }

  /**
   *  @brief Determines whether an element exists in a range.
   *  @ingroup binary_search_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __val     The search term.
   *  @param  __comp    A functor to use for comparisons.
   *  @return  True if @p __val (or its equivalent) is in @p [__first,__last].
   *
   *  Note that this does not actually return an iterator to @p __val.  For
   *  that, use std::find or a container's specialized find member functions.
   *
   *  The comparison function should have the same effects on ordering as
   *  the function used for the initial sort.
  */
  template<typename _ForwardIterator, typename _Tp, typename _Compare>
    bool
    binary_search(_ForwardIterator __first, _ForwardIterator __last,
                  const _Tp& __val, _Compare __comp)
    {
      typedef typename iterator_traits<_ForwardIterator>::value_type
	_ValueType;

      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _Tp, _ValueType>)
      __glibcxx_requires_partitioned_lower_pred(__first, __last,
						__val, __comp);
      __glibcxx_requires_partitioned_upper_pred(__first, __last,
						__val, __comp);

      _ForwardIterator __i = std::lower_bound(__first, __last, __val, __comp);
      return __i != __last && !bool(__comp(__val, *__i));
    }

  // merge

  /// This is a helper function for the __merge_adaptive routines.
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator>
    void
    __move_merge_adaptive(_InputIterator1 __first1, _InputIterator1 __last1,
			  _InputIterator2 __first2, _InputIterator2 __last2,
			  _OutputIterator __result)
    {
      while (__first1 != __last1 && __first2 != __last2)
	{
	  if (*__first2 < *__first1)
	    {
	      *__result = _GLIBCXX_MOVE(*__first2);
	      ++__first2;
	    }
	  else
	    {
	      *__result = _GLIBCXX_MOVE(*__first1);
	      ++__first1;
	    }
	  ++__result;
	}
      if (__first1 != __last1)
	_GLIBCXX_MOVE3(__first1, __last1, __result);
    }

  /// This is a helper function for the __merge_adaptive routines.
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator, typename _Compare>
    void
    __move_merge_adaptive(_InputIterator1 __first1, _InputIterator1 __last1,
			  _InputIterator2 __first2, _InputIterator2 __last2,
			  _OutputIterator __result, _Compare __comp)
    {
      while (__first1 != __last1 && __first2 != __last2)
	{
	  if (__comp(*__first2, *__first1))
	    {
	      *__result = _GLIBCXX_MOVE(*__first2);
	      ++__first2;
	    }
	  else
	    {
	      *__result = _GLIBCXX_MOVE(*__first1);
	      ++__first1;
	    }
	  ++__result;
	}
      if (__first1 != __last1)
	_GLIBCXX_MOVE3(__first1, __last1, __result);
    }

  /// This is a helper function for the __merge_adaptive routines.
  template<typename _BidirectionalIterator1, typename _BidirectionalIterator2,
	   typename _BidirectionalIterator3>
    void
    __move_merge_adaptive_backward(_BidirectionalIterator1 __first1,
				   _BidirectionalIterator1 __last1,
				   _BidirectionalIterator2 __first2,
				   _BidirectionalIterator2 __last2,
				   _BidirectionalIterator3 __result)
    {
      if (__first1 == __last1)
	{
	  _GLIBCXX_MOVE_BACKWARD3(__first2, __last2, __result);
	  return;
	}
      else if (__first2 == __last2)
	return;

      --__last1;
      --__last2;
      while (true)
	{
	  if (*__last2 < *__last1)
	    {
	      *--__result = _GLIBCXX_MOVE(*__last1);
	      if (__first1 == __last1)
		{
		  _GLIBCXX_MOVE_BACKWARD3(__first2, ++__last2, __result);
		  return;
		}
	      --__last1;
	    }
	  else
	    {
	      *--__result = _GLIBCXX_MOVE(*__last2);
	      if (__first2 == __last2)
		return;
	      --__last2;
	    }
	}
    }

  /// This is a helper function for the __merge_adaptive routines.
  template<typename _BidirectionalIterator1, typename _BidirectionalIterator2,
	   typename _BidirectionalIterator3, typename _Compare>
    void
    __move_merge_adaptive_backward(_BidirectionalIterator1 __first1,
				   _BidirectionalIterator1 __last1,
				   _BidirectionalIterator2 __first2,
				   _BidirectionalIterator2 __last2,
				   _BidirectionalIterator3 __result,
				   _Compare __comp)
    {
      if (__first1 == __last1)
	{
	  _GLIBCXX_MOVE_BACKWARD3(__first2, __last2, __result);
	  return;
	}
      else if (__first2 == __last2)
	return;

      --__last1;
      --__last2;
      while (true)
	{
	  if (__comp(*__last2, *__last1))
	    {
	      *--__result = _GLIBCXX_MOVE(*__last1);
	      if (__first1 == __last1)
		{
		  _GLIBCXX_MOVE_BACKWARD3(__first2, ++__last2, __result);
		  return;
		}
	      --__last1;
	    }
	  else
	    {
	      *--__result = _GLIBCXX_MOVE(*__last2);
	      if (__first2 == __last2)
		return;
	      --__last2;
	    }
	}
    }

  /// This is a helper function for the merge routines.
  template<typename _BidirectionalIterator1, typename _BidirectionalIterator2,
	   typename _Distance>
    _BidirectionalIterator1
    __rotate_adaptive(_BidirectionalIterator1 __first,
		      _BidirectionalIterator1 __middle,
		      _BidirectionalIterator1 __last,
		      _Distance __len1, _Distance __len2,
		      _BidirectionalIterator2 __buffer,
		      _Distance __buffer_size)
    {
      _BidirectionalIterator2 __buffer_end;
      if (__len1 > __len2 && __len2 <= __buffer_size)
	{
	  if (__len2)
	    {
	      __buffer_end = _GLIBCXX_MOVE3(__middle, __last, __buffer);
	      _GLIBCXX_MOVE_BACKWARD3(__first, __middle, __last);
	      return _GLIBCXX_MOVE3(__buffer, __buffer_end, __first);
	    }
	  else
	    return __first;
	}
      else if (__len1 <= __buffer_size)
	{
	  if (__len1)
	    {
	      __buffer_end = _GLIBCXX_MOVE3(__first, __middle, __buffer);
	      _GLIBCXX_MOVE3(__middle, __last, __first);
	      return _GLIBCXX_MOVE_BACKWARD3(__buffer, __buffer_end, __last);
	    }
	  else
	    return __last;
	}
      else
	{
	  std::rotate(__first, __middle, __last);
	  std::advance(__first, std::distance(__middle, __last));
	  return __first;
	}
    }

  /// This is a helper function for the merge routines.
  template<typename _BidirectionalIterator, typename _Distance,
	   typename _Pointer>
    void
    __merge_adaptive(_BidirectionalIterator __first,
                     _BidirectionalIterator __middle,
		     _BidirectionalIterator __last,
		     _Distance __len1, _Distance __len2,
		     _Pointer __buffer, _Distance __buffer_size)
    {
      if (__len1 <= __len2 && __len1 <= __buffer_size)
	{
	  _Pointer __buffer_end = _GLIBCXX_MOVE3(__first, __middle, __buffer);
	  std::__move_merge_adaptive(__buffer, __buffer_end, __middle, __last,
				     __first);
	}
      else if (__len2 <= __buffer_size)
	{
	  _Pointer __buffer_end = _GLIBCXX_MOVE3(__middle, __last, __buffer);
	  std::__move_merge_adaptive_backward(__first, __middle, __buffer,
					      __buffer_end, __last);
	}
      else
	{
	  _BidirectionalIterator __first_cut = __first;
	  _BidirectionalIterator __second_cut = __middle;
	  _Distance __len11 = 0;
	  _Distance __len22 = 0;
	  if (__len1 > __len2)
	    {
	      __len11 = __len1 / 2;
	      std::advance(__first_cut, __len11);
	      __second_cut = std::lower_bound(__middle, __last,
					      *__first_cut);
	      __len22 = std::distance(__middle, __second_cut);
	    }
	  else
	    {
	      __len22 = __len2 / 2;
	      std::advance(__second_cut, __len22);
	      __first_cut = std::upper_bound(__first, __middle,
					     *__second_cut);
	      __len11 = std::distance(__first, __first_cut);
	    }
	  _BidirectionalIterator __new_middle =
	    std::__rotate_adaptive(__first_cut, __middle, __second_cut,
				   __len1 - __len11, __len22, __buffer,
				   __buffer_size);
	  std::__merge_adaptive(__first, __first_cut, __new_middle, __len11,
				__len22, __buffer, __buffer_size);
	  std::__merge_adaptive(__new_middle, __second_cut, __last,
				__len1 - __len11,
				__len2 - __len22, __buffer, __buffer_size);
	}
    }

  /// This is a helper function for the merge routines.
  template<typename _BidirectionalIterator, typename _Distance, 
	   typename _Pointer, typename _Compare>
    void
    __merge_adaptive(_BidirectionalIterator __first,
                     _BidirectionalIterator __middle,
		     _BidirectionalIterator __last,
		     _Distance __len1, _Distance __len2,
		     _Pointer __buffer, _Distance __buffer_size,
		     _Compare __comp)
    {
      if (__len1 <= __len2 && __len1 <= __buffer_size)
	{
	  _Pointer __buffer_end = _GLIBCXX_MOVE3(__first, __middle, __buffer);
	  std::__move_merge_adaptive(__buffer, __buffer_end, __middle, __last,
				     __first, __comp);
	}
      else if (__len2 <= __buffer_size)
	{
	  _Pointer __buffer_end = _GLIBCXX_MOVE3(__middle, __last, __buffer);
	  std::__move_merge_adaptive_backward(__first, __middle, __buffer,
					      __buffer_end, __last, __comp);
	}
      else
	{
	  _BidirectionalIterator __first_cut = __first;
	  _BidirectionalIterator __second_cut = __middle;
	  _Distance __len11 = 0;
	  _Distance __len22 = 0;
	  if (__len1 > __len2)
	    {
	      __len11 = __len1 / 2;
	      std::advance(__first_cut, __len11);
	      __second_cut = std::lower_bound(__middle, __last, *__first_cut,
					      __comp);
	      __len22 = std::distance(__middle, __second_cut);
	    }
	  else
	    {
	      __len22 = __len2 / 2;
	      std::advance(__second_cut, __len22);
	      __first_cut = std::upper_bound(__first, __middle, *__second_cut,
					     __comp);
	      __len11 = std::distance(__first, __first_cut);
	    }
	  _BidirectionalIterator __new_middle =
	    std::__rotate_adaptive(__first_cut, __middle, __second_cut,
				   __len1 - __len11, __len22, __buffer,
				   __buffer_size);
	  std::__merge_adaptive(__first, __first_cut, __new_middle, __len11,
				__len22, __buffer, __buffer_size, __comp);
	  std::__merge_adaptive(__new_middle, __second_cut, __last,
				__len1 - __len11,
				__len2 - __len22, __buffer,
				__buffer_size, __comp);
	}
    }

  /// This is a helper function for the merge routines.
  template<typename _BidirectionalIterator, typename _Distance>
    void
    __merge_without_buffer(_BidirectionalIterator __first,
			   _BidirectionalIterator __middle,
			   _BidirectionalIterator __last,
			   _Distance __len1, _Distance __len2)
    {
      if (__len1 == 0 || __len2 == 0)
	return;
      if (__len1 + __len2 == 2)
	{
	  if (*__middle < *__first)
	    std::iter_swap(__first, __middle);
	  return;
	}
      _BidirectionalIterator __first_cut = __first;
      _BidirectionalIterator __second_cut = __middle;
      _Distance __len11 = 0;
      _Distance __len22 = 0;
      if (__len1 > __len2)
	{
	  __len11 = __len1 / 2;
	  std::advance(__first_cut, __len11);
	  __second_cut = std::lower_bound(__middle, __last, *__first_cut);
	  __len22 = std::distance(__middle, __second_cut);
	}
      else
	{
	  __len22 = __len2 / 2;
	  std::advance(__second_cut, __len22);
	  __first_cut = std::upper_bound(__first, __middle, *__second_cut);
	  __len11 = std::distance(__first, __first_cut);
	}
      std::rotate(__first_cut, __middle, __second_cut);
      _BidirectionalIterator __new_middle = __first_cut;
      std::advance(__new_middle, std::distance(__middle, __second_cut));
      std::__merge_without_buffer(__first, __first_cut, __new_middle,
				  __len11, __len22);
      std::__merge_without_buffer(__new_middle, __second_cut, __last,
				  __len1 - __len11, __len2 - __len22);
    }

  /// This is a helper function for the merge routines.
  template<typename _BidirectionalIterator, typename _Distance,
	   typename _Compare>
    void
    __merge_without_buffer(_BidirectionalIterator __first,
                           _BidirectionalIterator __middle,
			   _BidirectionalIterator __last,
			   _Distance __len1, _Distance __len2,
			   _Compare __comp)
    {
      if (__len1 == 0 || __len2 == 0)
	return;
      if (__len1 + __len2 == 2)
	{
	  if (__comp(*__middle, *__first))
	    std::iter_swap(__first, __middle);
	  return;
	}
      _BidirectionalIterator __first_cut = __first;
      _BidirectionalIterator __second_cut = __middle;
      _Distance __len11 = 0;
      _Distance __len22 = 0;
      if (__len1 > __len2)
	{
	  __len11 = __len1 / 2;
	  std::advance(__first_cut, __len11);
	  __second_cut = std::lower_bound(__middle, __last, *__first_cut,
					  __comp);
	  __len22 = std::distance(__middle, __second_cut);
	}
      else
	{
	  __len22 = __len2 / 2;
	  std::advance(__second_cut, __len22);
	  __first_cut = std::upper_bound(__first, __middle, *__second_cut,
					 __comp);
	  __len11 = std::distance(__first, __first_cut);
	}
      std::rotate(__first_cut, __middle, __second_cut);
      _BidirectionalIterator __new_middle = __first_cut;
      std::advance(__new_middle, std::distance(__middle, __second_cut));
      std::__merge_without_buffer(__first, __first_cut, __new_middle,
				  __len11, __len22, __comp);
      std::__merge_without_buffer(__new_middle, __second_cut, __last,
				  __len1 - __len11, __len2 - __len22, __comp);
    }

  /**
   *  @brief Merges two sorted ranges in place.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __middle  Another iterator.
   *  @param  __last    Another iterator.
   *  @return  Nothing.
   *
   *  Merges two sorted and consecutive ranges, [__first,__middle) and
   *  [__middle,__last), and puts the result in [__first,__last).  The
   *  output will be sorted.  The sort is @e stable, that is, for
   *  equivalent elements in the two ranges, elements from the first
   *  range will always come before elements from the second.
   *
   *  If enough additional memory is available, this takes (__last-__first)-1
   *  comparisons.  Otherwise an NlogN algorithm is used, where N is
   *  distance(__first,__last).
  */
  template<typename _BidirectionalIterator>
    void
    inplace_merge(_BidirectionalIterator __first,
		  _BidirectionalIterator __middle,
		  _BidirectionalIterator __last)
    {
      typedef typename iterator_traits<_BidirectionalIterator>::value_type
          _ValueType;
      typedef typename iterator_traits<_BidirectionalIterator>::difference_type
          _DistanceType;

      // concept requirements
      __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
	    _BidirectionalIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<_ValueType>)
      __glibcxx_requires_sorted(__first, __middle);
      __glibcxx_requires_sorted(__middle, __last);

      if (__first == __middle || __middle == __last)
	return;

      _DistanceType __len1 = std::distance(__first, __middle);
      _DistanceType __len2 = std::distance(__middle, __last);

      _Temporary_buffer<_BidirectionalIterator, _ValueType> __buf(__first,
								  __last);
      if (__buf.begin() == 0)
	std::__merge_without_buffer(__first, __middle, __last, __len1, __len2);
      else
	std::__merge_adaptive(__first, __middle, __last, __len1, __len2,
			      __buf.begin(), _DistanceType(__buf.size()));
    }

  /**
   *  @brief Merges two sorted ranges in place.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __middle  Another iterator.
   *  @param  __last    Another iterator.
   *  @param  __comp    A functor to use for comparisons.
   *  @return  Nothing.
   *
   *  Merges two sorted and consecutive ranges, [__first,__middle) and
   *  [middle,last), and puts the result in [__first,__last).  The output will
   *  be sorted.  The sort is @e stable, that is, for equivalent
   *  elements in the two ranges, elements from the first range will always
   *  come before elements from the second.
   *
   *  If enough additional memory is available, this takes (__last-__first)-1
   *  comparisons.  Otherwise an NlogN algorithm is used, where N is
   *  distance(__first,__last).
   *
   *  The comparison function should have the same effects on ordering as
   *  the function used for the initial sort.
  */
  template<typename _BidirectionalIterator, typename _Compare>
    void
    inplace_merge(_BidirectionalIterator __first,
		  _BidirectionalIterator __middle,
		  _BidirectionalIterator __last,
		  _Compare __comp)
    {
      typedef typename iterator_traits<_BidirectionalIterator>::value_type
          _ValueType;
      typedef typename iterator_traits<_BidirectionalIterator>::difference_type
          _DistanceType;

      // concept requirements
      __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
	    _BidirectionalIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
	    _ValueType, _ValueType>)
      __glibcxx_requires_sorted_pred(__first, __middle, __comp);
      __glibcxx_requires_sorted_pred(__middle, __last, __comp);

      if (__first == __middle || __middle == __last)
	return;

      const _DistanceType __len1 = std::distance(__first, __middle);
      const _DistanceType __len2 = std::distance(__middle, __last);

      _Temporary_buffer<_BidirectionalIterator, _ValueType> __buf(__first,
								  __last);
      if (__buf.begin() == 0)
	std::__merge_without_buffer(__first, __middle, __last, __len1,
				    __len2, __comp);
      else
	std::__merge_adaptive(__first, __middle, __last, __len1, __len2,
			      __buf.begin(), _DistanceType(__buf.size()),
			      __comp);
    }


  /// This is a helper function for the __merge_sort_loop routines.
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator>
    _OutputIterator
    __move_merge(_InputIterator1 __first1, _InputIterator1 __last1,
		 _InputIterator2 __first2, _InputIterator2 __last2,
		 _OutputIterator __result)
    {
      while (__first1 != __last1 && __first2 != __last2)
	{
	  if (*__first2 < *__first1)
	    {
	      *__result = _GLIBCXX_MOVE(*__first2);
	      ++__first2;
	    }
	  else
	    {
	      *__result = _GLIBCXX_MOVE(*__first1);
	      ++__first1;
	    }
	  ++__result;
	}
      return _GLIBCXX_MOVE3(__first2, __last2,
			    _GLIBCXX_MOVE3(__first1, __last1,
					   __result));
    }

  /// This is a helper function for the __merge_sort_loop routines.
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator, typename _Compare>
    _OutputIterator
    __move_merge(_InputIterator1 __first1, _InputIterator1 __last1,
		 _InputIterator2 __first2, _InputIterator2 __last2,
		 _OutputIterator __result, _Compare __comp)
    {
      while (__first1 != __last1 && __first2 != __last2)
	{
	  if (__comp(*__first2, *__first1))
	    {
	      *__result = _GLIBCXX_MOVE(*__first2);
	      ++__first2;
	    }
	  else
	    {
	      *__result = _GLIBCXX_MOVE(*__first1);
	      ++__first1;
	    }
	  ++__result;
	}
      return _GLIBCXX_MOVE3(__first2, __last2,
			    _GLIBCXX_MOVE3(__first1, __last1,
					   __result));
    }

  template<typename _RandomAccessIterator1, typename _RandomAccessIterator2,
	   typename _Distance>
    void
    __merge_sort_loop(_RandomAccessIterator1 __first,
		      _RandomAccessIterator1 __last,
		      _RandomAccessIterator2 __result,
		      _Distance __step_size)
    {
      const _Distance __two_step = 2 * __step_size;

      while (__last - __first >= __two_step)
	{
	  __result = std::__move_merge(__first, __first + __step_size,
				       __first + __step_size,
				       __first + __two_step, __result);
	  __first += __two_step;
	}

      __step_size = std::min(_Distance(__last - __first), __step_size);
      std::__move_merge(__first, __first + __step_size,
			__first + __step_size, __last, __result);
    }

  template<typename _RandomAccessIterator1, typename _RandomAccessIterator2,
	   typename _Distance, typename _Compare>
    void
    __merge_sort_loop(_RandomAccessIterator1 __first,
		      _RandomAccessIterator1 __last,
		      _RandomAccessIterator2 __result, _Distance __step_size,
		      _Compare __comp)
    {
      const _Distance __two_step = 2 * __step_size;

      while (__last - __first >= __two_step)
	{
	  __result = std::__move_merge(__first, __first + __step_size,
				       __first + __step_size,
				       __first + __two_step,
				       __result, __comp);
	  __first += __two_step;
	}
      __step_size = std::min(_Distance(__last - __first), __step_size);

      std::__move_merge(__first,__first + __step_size,
			__first + __step_size, __last, __result, __comp);
    }

  template<typename _RandomAccessIterator, typename _Distance>
    void
    __chunk_insertion_sort(_RandomAccessIterator __first,
			   _RandomAccessIterator __last,
			   _Distance __chunk_size)
    {
      while (__last - __first >= __chunk_size)
	{
	  std::__insertion_sort(__first, __first + __chunk_size);
	  __first += __chunk_size;
	}
      std::__insertion_sort(__first, __last);
    }

  template<typename _RandomAccessIterator, typename _Distance,
	   typename _Compare>
    void
    __chunk_insertion_sort(_RandomAccessIterator __first,
			   _RandomAccessIterator __last,
			   _Distance __chunk_size, _Compare __comp)
    {
      while (__last - __first >= __chunk_size)
	{
	  std::__insertion_sort(__first, __first + __chunk_size, __comp);
	  __first += __chunk_size;
	}
      std::__insertion_sort(__first, __last, __comp);
    }

  enum { _S_chunk_size = 7 };

  template<typename _RandomAccessIterator, typename _Pointer>
    void
    __merge_sort_with_buffer(_RandomAccessIterator __first,
			     _RandomAccessIterator __last,
                             _Pointer __buffer)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::difference_type
	_Distance;

      const _Distance __len = __last - __first;
      const _Pointer __buffer_last = __buffer + __len;

      _Distance __step_size = _S_chunk_size;
      std::__chunk_insertion_sort(__first, __last, __step_size);

      while (__step_size < __len)
	{
	  std::__merge_sort_loop(__first, __last, __buffer, __step_size);
	  __step_size *= 2;
	  std::__merge_sort_loop(__buffer, __buffer_last, __first, __step_size);
	  __step_size *= 2;
	}
    }

  template<typename _RandomAccessIterator, typename _Pointer, typename _Compare>
    void
    __merge_sort_with_buffer(_RandomAccessIterator __first,
			     _RandomAccessIterator __last,
                             _Pointer __buffer, _Compare __comp)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::difference_type
	_Distance;

      const _Distance __len = __last - __first;
      const _Pointer __buffer_last = __buffer + __len;

      _Distance __step_size = _S_chunk_size;
      std::__chunk_insertion_sort(__first, __last, __step_size, __comp);

      while (__step_size < __len)
	{
	  std::__merge_sort_loop(__first, __last, __buffer,
				 __step_size, __comp);
	  __step_size *= 2;
	  std::__merge_sort_loop(__buffer, __buffer_last, __first,
				 __step_size, __comp);
	  __step_size *= 2;
	}
    }

  template<typename _RandomAccessIterator, typename _Pointer,
	   typename _Distance>
    void
    __stable_sort_adaptive(_RandomAccessIterator __first,
			   _RandomAccessIterator __last,
                           _Pointer __buffer, _Distance __buffer_size)
    {
      const _Distance __len = (__last - __first + 1) / 2;
      const _RandomAccessIterator __middle = __first + __len;
      if (__len > __buffer_size)
	{
	  std::__stable_sort_adaptive(__first, __middle,
				      __buffer, __buffer_size);
	  std::__stable_sort_adaptive(__middle, __last,
				      __buffer, __buffer_size);
	}
      else
	{
	  std::__merge_sort_with_buffer(__first, __middle, __buffer);
	  std::__merge_sort_with_buffer(__middle, __last, __buffer);
	}
      std::__merge_adaptive(__first, __middle, __last,
			    _Distance(__middle - __first),
			    _Distance(__last - __middle),
			    __buffer, __buffer_size);
    }

  template<typename _RandomAccessIterator, typename _Pointer,
	   typename _Distance, typename _Compare>
    void
    __stable_sort_adaptive(_RandomAccessIterator __first,
			   _RandomAccessIterator __last,
                           _Pointer __buffer, _Distance __buffer_size,
                           _Compare __comp)
    {
      const _Distance __len = (__last - __first + 1) / 2;
      const _RandomAccessIterator __middle = __first + __len;
      if (__len > __buffer_size)
	{
	  std::__stable_sort_adaptive(__first, __middle, __buffer,
				      __buffer_size, __comp);
	  std::__stable_sort_adaptive(__middle, __last, __buffer,
				      __buffer_size, __comp);
	}
      else
	{
	  std::__merge_sort_with_buffer(__first, __middle, __buffer, __comp);
	  std::__merge_sort_with_buffer(__middle, __last, __buffer, __comp);
	}
      std::__merge_adaptive(__first, __middle, __last,
			    _Distance(__middle - __first),
			    _Distance(__last - __middle),
			    __buffer, __buffer_size,
			    __comp);
    }

  /// This is a helper function for the stable sorting routines.
  template<typename _RandomAccessIterator>
    void
    __inplace_stable_sort(_RandomAccessIterator __first,
			  _RandomAccessIterator __last)
    {
      if (__last - __first < 15)
	{
	  std::__insertion_sort(__first, __last);
	  return;
	}
      _RandomAccessIterator __middle = __first + (__last - __first) / 2;
      std::__inplace_stable_sort(__first, __middle);
      std::__inplace_stable_sort(__middle, __last);
      std::__merge_without_buffer(__first, __middle, __last,
				  __middle - __first,
				  __last - __middle);
    }

  /// This is a helper function for the stable sorting routines.
  template<typename _RandomAccessIterator, typename _Compare>
    void
    __inplace_stable_sort(_RandomAccessIterator __first,
			  _RandomAccessIterator __last, _Compare __comp)
    {
      if (__last - __first < 15)
	{
	  std::__insertion_sort(__first, __last, __comp);
	  return;
	}
      _RandomAccessIterator __middle = __first + (__last - __first) / 2;
      std::__inplace_stable_sort(__first, __middle, __comp);
      std::__inplace_stable_sort(__middle, __last, __comp);
      std::__merge_without_buffer(__first, __middle, __last,
				  __middle - __first,
				  __last - __middle,
				  __comp);
    }

  // stable_sort

  // Set algorithms: includes, set_union, set_intersection, set_difference,
  // set_symmetric_difference.  All of these algorithms have the precondition
  // that their input ranges are sorted and the postcondition that their output
  // ranges are sorted.

  /**
   *  @brief Determines whether all elements of a sequence exists in a range.
   *  @param  __first1  Start of search range.
   *  @param  __last1   End of search range.
   *  @param  __first2  Start of sequence
   *  @param  __last2   End of sequence.
   *  @return  True if each element in [__first2,__last2) is contained in order
   *  within [__first1,__last1).  False otherwise.
   *  @ingroup set_algorithms
   *
   *  This operation expects both [__first1,__last1) and
   *  [__first2,__last2) to be sorted.  Searches for the presence of
   *  each element in [__first2,__last2) within [__first1,__last1).
   *  The iterators over each range only move forward, so this is a
   *  linear algorithm.  If an element in [__first2,__last2) is not
   *  found before the search iterator reaches @p __last2, false is
   *  returned.
  */
  template<typename _InputIterator1, typename _InputIterator2>
    bool
    includes(_InputIterator1 __first1, _InputIterator1 __last1,
	     _InputIterator2 __first2, _InputIterator2 __last2)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType1, _ValueType2>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType2, _ValueType1>)
      __glibcxx_requires_sorted_set(__first1, __last1, __first2);
      __glibcxx_requires_sorted_set(__first2, __last2, __first1);

      while (__first1 != __last1 && __first2 != __last2)
	if (*__first2 < *__first1)
	  return false;
	else if(*__first1 < *__first2)
	  ++__first1;
	else
	  ++__first1, ++__first2;

      return __first2 == __last2;
    }

  /**
   *  @brief Determines whether all elements of a sequence exists in a range
   *  using comparison.
   *  @ingroup set_algorithms
   *  @param  __first1  Start of search range.
   *  @param  __last1   End of search range.
   *  @param  __first2  Start of sequence
   *  @param  __last2   End of sequence.
   *  @param  __comp    Comparison function to use.
   *  @return True if each element in [__first2,__last2) is contained
   *  in order within [__first1,__last1) according to comp.  False
   *  otherwise.  @ingroup set_algorithms
   *
   *  This operation expects both [__first1,__last1) and
   *  [__first2,__last2) to be sorted.  Searches for the presence of
   *  each element in [__first2,__last2) within [__first1,__last1),
   *  using comp to decide.  The iterators over each range only move
   *  forward, so this is a linear algorithm.  If an element in
   *  [__first2,__last2) is not found before the search iterator
   *  reaches @p __last2, false is returned.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _Compare>
    bool
    includes(_InputIterator1 __first1, _InputIterator1 __last1,
	     _InputIterator2 __first2, _InputIterator2 __last2,
	     _Compare __comp)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType1, _ValueType2>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType2, _ValueType1>)
      __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
      __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);

      while (__first1 != __last1 && __first2 != __last2)
	if (__comp(*__first2, *__first1))
	  return false;
	else if(__comp(*__first1, *__first2))
	  ++__first1;
	else
	  ++__first1, ++__first2;

      return __first2 == __last2;
    }

  // nth_element
  // merge
  // set_difference
  // set_intersection
  // set_union
  // stable_sort
  // set_symmetric_difference
  // min_element
  // max_element

  /**
   *  @brief  Permute range into the next @e dictionary ordering.
   *  @ingroup sorting_algorithms
   *  @param  __first  Start of range.
   *  @param  __last   End of range.
   *  @return  False if wrapped to first permutation, true otherwise.
   *
   *  Treats all permutations of the range as a set of @e dictionary sorted
   *  sequences.  Permutes the current sequence into the next one of this set.
   *  Returns true if there are more sequences to generate.  If the sequence
   *  is the largest of the set, the smallest is generated and false returned.
  */
  template<typename _BidirectionalIterator>
    bool
    next_permutation(_BidirectionalIterator __first,
		     _BidirectionalIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<
	    typename iterator_traits<_BidirectionalIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return false;
      _BidirectionalIterator __i = __first;
      ++__i;
      if (__i == __last)
	return false;
      __i = __last;
      --__i;

      for(;;)
	{
	  _BidirectionalIterator __ii = __i;
	  --__i;
	  if (*__i < *__ii)
	    {
	      _BidirectionalIterator __j = __last;
	      while (!(*__i < *--__j))
		{}
	      std::iter_swap(__i, __j);
	      std::reverse(__ii, __last);
	      return true;
	    }
	  if (__i == __first)
	    {
	      std::reverse(__first, __last);
	      return false;
	    }
	}
    }

  /**
   *  @brief  Permute range into the next @e dictionary ordering using
   *          comparison functor.
   *  @ingroup sorting_algorithms
   *  @param  __first  Start of range.
   *  @param  __last   End of range.
   *  @param  __comp   A comparison functor.
   *  @return  False if wrapped to first permutation, true otherwise.
   *
   *  Treats all permutations of the range [__first,__last) as a set of
   *  @e dictionary sorted sequences ordered by @p __comp.  Permutes the current
   *  sequence into the next one of this set.  Returns true if there are more
   *  sequences to generate.  If the sequence is the largest of the set, the
   *  smallest is generated and false returned.
  */
  template<typename _BidirectionalIterator, typename _Compare>
    bool
    next_permutation(_BidirectionalIterator __first,
		     _BidirectionalIterator __last, _Compare __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
	    typename iterator_traits<_BidirectionalIterator>::value_type,
	    typename iterator_traits<_BidirectionalIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return false;
      _BidirectionalIterator __i = __first;
      ++__i;
      if (__i == __last)
	return false;
      __i = __last;
      --__i;

      for(;;)
	{
	  _BidirectionalIterator __ii = __i;
	  --__i;
	  if (__comp(*__i, *__ii))
	    {
	      _BidirectionalIterator __j = __last;
	      while (!bool(__comp(*__i, *--__j)))
		{}
	      std::iter_swap(__i, __j);
	      std::reverse(__ii, __last);
	      return true;
	    }
	  if (__i == __first)
	    {
	      std::reverse(__first, __last);
	      return false;
	    }
	}
    }

  /**
   *  @brief  Permute range into the previous @e dictionary ordering.
   *  @ingroup sorting_algorithms
   *  @param  __first  Start of range.
   *  @param  __last   End of range.
   *  @return  False if wrapped to last permutation, true otherwise.
   *
   *  Treats all permutations of the range as a set of @e dictionary sorted
   *  sequences.  Permutes the current sequence into the previous one of this
   *  set.  Returns true if there are more sequences to generate.  If the
   *  sequence is the smallest of the set, the largest is generated and false
   *  returned.
  */
  template<typename _BidirectionalIterator>
    bool
    prev_permutation(_BidirectionalIterator __first,
		     _BidirectionalIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<
	    typename iterator_traits<_BidirectionalIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return false;
      _BidirectionalIterator __i = __first;
      ++__i;
      if (__i == __last)
	return false;
      __i = __last;
      --__i;

      for(;;)
	{
	  _BidirectionalIterator __ii = __i;
	  --__i;
	  if (*__ii < *__i)
	    {
	      _BidirectionalIterator __j = __last;
	      while (!(*--__j < *__i))
		{}
	      std::iter_swap(__i, __j);
	      std::reverse(__ii, __last);
	      return true;
	    }
	  if (__i == __first)
	    {
	      std::reverse(__first, __last);
	      return false;
	    }
	}
    }

  /**
   *  @brief  Permute range into the previous @e dictionary ordering using
   *          comparison functor.
   *  @ingroup sorting_algorithms
   *  @param  __first  Start of range.
   *  @param  __last   End of range.
   *  @param  __comp   A comparison functor.
   *  @return  False if wrapped to last permutation, true otherwise.
   *
   *  Treats all permutations of the range [__first,__last) as a set of
   *  @e dictionary sorted sequences ordered by @p __comp.  Permutes the current
   *  sequence into the previous one of this set.  Returns true if there are
   *  more sequences to generate.  If the sequence is the smallest of the set,
   *  the largest is generated and false returned.
  */
  template<typename _BidirectionalIterator, typename _Compare>
    bool
    prev_permutation(_BidirectionalIterator __first,
		     _BidirectionalIterator __last, _Compare __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_BidirectionalIteratorConcept<
				  _BidirectionalIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
	    typename iterator_traits<_BidirectionalIterator>::value_type,
	    typename iterator_traits<_BidirectionalIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return false;
      _BidirectionalIterator __i = __first;
      ++__i;
      if (__i == __last)
	return false;
      __i = __last;
      --__i;

      for(;;)
	{
	  _BidirectionalIterator __ii = __i;
	  --__i;
	  if (__comp(*__ii, *__i))
	    {
	      _BidirectionalIterator __j = __last;
	      while (!bool(__comp(*--__j, *__i)))
		{}
	      std::iter_swap(__i, __j);
	      std::reverse(__ii, __last);
	      return true;
	    }
	  if (__i == __first)
	    {
	      std::reverse(__first, __last);
	      return false;
	    }
	}
    }

  // replace
  // replace_if

  /**
   *  @brief Copy a sequence, replacing each element of one value with another
   *         value.
   *  @param  __first      An input iterator.
   *  @param  __last       An input iterator.
   *  @param  __result     An output iterator.
   *  @param  __old_value  The value to be replaced.
   *  @param  __new_value  The replacement value.
   *  @return   The end of the output sequence, @p result+(last-first).
   *
   *  Copies each element in the input range @p [__first,__last) to the
   *  output range @p [__result,__result+(__last-__first)) replacing elements
   *  equal to @p __old_value with @p __new_value.
  */
  template<typename _InputIterator, typename _OutputIterator, typename _Tp>
    _OutputIterator
    replace_copy(_InputIterator __first, _InputIterator __last,
		 _OutputIterator __result,
		 const _Tp& __old_value, const _Tp& __new_value)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_function_requires(_EqualOpConcept<
	    typename iterator_traits<_InputIterator>::value_type, _Tp>)
      __glibcxx_requires_valid_range(__first, __last);

      for (; __first != __last; ++__first, ++__result)
	if (*__first == __old_value)
	  *__result = __new_value;
	else
	  *__result = *__first;
      return __result;
    }

  /**
   *  @brief Copy a sequence, replacing each value for which a predicate
   *         returns true with another value.
   *  @ingroup mutating_algorithms
   *  @param  __first      An input iterator.
   *  @param  __last       An input iterator.
   *  @param  __result     An output iterator.
   *  @param  __pred       A predicate.
   *  @param  __new_value  The replacement value.
   *  @return   The end of the output sequence, @p __result+(__last-__first).
   *
   *  Copies each element in the range @p [__first,__last) to the range
   *  @p [__result,__result+(__last-__first)) replacing elements for which
   *  @p __pred returns true with @p __new_value.
  */
  template<typename _InputIterator, typename _OutputIterator,
	   typename _Predicate, typename _Tp>
    _OutputIterator
    replace_copy_if(_InputIterator __first, _InputIterator __last,
		    _OutputIterator __result,
		    _Predicate __pred, const _Tp& __new_value)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      for (; __first != __last; ++__first, ++__result)
	if (__pred(*__first))
	  *__result = __new_value;
	else
	  *__result = *__first;
      return __result;
    }

#if __cplusplus >= 201103L
  /**
   *  @brief  Determines whether the elements of a sequence are sorted.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @return  True if the elements are sorted, false otherwise.
  */
  template<typename _ForwardIterator>
    inline bool
    is_sorted(_ForwardIterator __first, _ForwardIterator __last)
    { return std::is_sorted_until(__first, __last) == __last; }

  /**
   *  @brief  Determines whether the elements of a sequence are sorted
   *          according to a comparison functor.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __comp    A comparison functor.
   *  @return  True if the elements are sorted, false otherwise.
  */
  template<typename _ForwardIterator, typename _Compare>
    inline bool
    is_sorted(_ForwardIterator __first, _ForwardIterator __last,
	      _Compare __comp)
    { return std::is_sorted_until(__first, __last, __comp) == __last; }

  /**
   *  @brief  Determines the end of a sorted sequence.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @return  An iterator pointing to the last iterator i in [__first, __last)
   *           for which the range [__first, i) is sorted.
  */
  template<typename _ForwardIterator>
    _ForwardIterator
    is_sorted_until(_ForwardIterator __first, _ForwardIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return __last;

      _ForwardIterator __next = __first;
      for (++__next; __next != __last; __first = __next, ++__next)
	if (*__next < *__first)
	  return __next;
      return __next;
    }

  /**
   *  @brief  Determines the end of a sorted sequence using comparison functor.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __comp    A comparison functor.
   *  @return  An iterator pointing to the last iterator i in [__first, __last)
   *           for which the range [__first, i) is sorted.
  */
  template<typename _ForwardIterator, typename _Compare>
    _ForwardIterator
    is_sorted_until(_ForwardIterator __first, _ForwardIterator __last,
		    _Compare __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
	    typename iterator_traits<_ForwardIterator>::value_type,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return __last;

      _ForwardIterator __next = __first;
      for (++__next; __next != __last; __first = __next, ++__next)
	if (__comp(*__next, *__first))
	  return __next;
      return __next;
    }

  /**
   *  @brief  Determines min and max at once as an ordered pair.
   *  @ingroup sorting_algorithms
   *  @param  __a  A thing of arbitrary type.
   *  @param  __b  Another thing of arbitrary type.
   *  @return A pair(__b, __a) if __b is smaller than __a, pair(__a,
   *  __b) otherwise.
  */
  template<typename _Tp>
    inline pair<const _Tp&, const _Tp&>
    minmax(const _Tp& __a, const _Tp& __b)
    {
      // concept requirements
      __glibcxx_function_requires(_LessThanComparableConcept<_Tp>)

      return __b < __a ? pair<const _Tp&, const _Tp&>(__b, __a)
	               : pair<const _Tp&, const _Tp&>(__a, __b);
    }

  /**
   *  @brief  Determines min and max at once as an ordered pair.
   *  @ingroup sorting_algorithms
   *  @param  __a  A thing of arbitrary type.
   *  @param  __b  Another thing of arbitrary type.
   *  @param  __comp  A @link comparison_functors comparison functor @endlink.
   *  @return A pair(__b, __a) if __b is smaller than __a, pair(__a,
   *  __b) otherwise.
  */
  template<typename _Tp, typename _Compare>
    inline pair<const _Tp&, const _Tp&>
    minmax(const _Tp& __a, const _Tp& __b, _Compare __comp)
    {
      return __comp(__b, __a) ? pair<const _Tp&, const _Tp&>(__b, __a)
	                      : pair<const _Tp&, const _Tp&>(__a, __b);
    }

  /**
   *  @brief  Return a pair of iterators pointing to the minimum and maximum
   *          elements in a range.
   *  @ingroup sorting_algorithms
   *  @param  __first  Start of range.
   *  @param  __last   End of range.
   *  @return  make_pair(m, M), where m is the first iterator i in 
   *           [__first, __last) such that no other element in the range is
   *           smaller, and where M is the last iterator i in [__first, __last)
   *           such that no other element in the range is larger.
  */
  template<typename _ForwardIterator>
    pair<_ForwardIterator, _ForwardIterator>
    minmax_element(_ForwardIterator __first, _ForwardIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      _ForwardIterator __next = __first;
      if (__first == __last
	  || ++__next == __last)
	return std::make_pair(__first, __first);

      _ForwardIterator __min, __max;
      if (*__next < *__first)
	{
	  __min = __next;
	  __max = __first;
	}
      else
	{
	  __min = __first;
	  __max = __next;
	}

      __first = __next;
      ++__first;

      while (__first != __last)
	{
	  __next = __first;
	  if (++__next == __last)
	    {
	      if (*__first < *__min)
		__min = __first;
	      else if (!(*__first < *__max))
		__max = __first;
	      break;
	    }

	  if (*__next < *__first)
	    {
	      if (*__next < *__min)
		__min = __next;
	      if (!(*__first < *__max))
		__max = __first;
	    }
	  else
	    {
	      if (*__first < *__min)
		__min = __first;
	      if (!(*__next < *__max))
		__max = __next;
	    }

	  __first = __next;
	  ++__first;
	}

      return std::make_pair(__min, __max);
    }

  /**
   *  @brief  Return a pair of iterators pointing to the minimum and maximum
   *          elements in a range.
   *  @ingroup sorting_algorithms
   *  @param  __first  Start of range.
   *  @param  __last   End of range.
   *  @param  __comp   Comparison functor.
   *  @return  make_pair(m, M), where m is the first iterator i in 
   *           [__first, __last) such that no other element in the range is
   *           smaller, and where M is the last iterator i in [__first, __last)
   *           such that no other element in the range is larger.
  */
  template<typename _ForwardIterator, typename _Compare>
    pair<_ForwardIterator, _ForwardIterator>
    minmax_element(_ForwardIterator __first, _ForwardIterator __last,
		   _Compare __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
	    typename iterator_traits<_ForwardIterator>::value_type,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      _ForwardIterator __next = __first;
      if (__first == __last
	  || ++__next == __last)
	return std::make_pair(__first, __first);

      _ForwardIterator __min, __max;
      if (__comp(*__next, *__first))
	{
	  __min = __next;
	  __max = __first;
	}
      else
	{
	  __min = __first;
	  __max = __next;
	}

      __first = __next;
      ++__first;

      while (__first != __last)
	{
	  __next = __first;
	  if (++__next == __last)
	    {
	      if (__comp(*__first, *__min))
		__min = __first;
	      else if (!__comp(*__first, *__max))
		__max = __first;
	      break;
	    }

	  if (__comp(*__next, *__first))
	    {
	      if (__comp(*__next, *__min))
		__min = __next;
	      if (!__comp(*__first, *__max))
		__max = __first;
	    }
	  else
	    {
	      if (__comp(*__first, *__min))
		__min = __first;
	      if (!__comp(*__next, *__max))
		__max = __next;
	    }

	  __first = __next;
	  ++__first;
	}

      return std::make_pair(__min, __max);
    }

  // N2722 + DR 915.
  template<typename _Tp>
    inline _Tp
    min(initializer_list<_Tp> __l)
    { return *std::min_element(__l.begin(), __l.end()); }

  template<typename _Tp, typename _Compare>
    inline _Tp
    min(initializer_list<_Tp> __l, _Compare __comp)
    { return *std::min_element(__l.begin(), __l.end(), __comp); }

  template<typename _Tp>
    inline _Tp
    max(initializer_list<_Tp> __l)
    { return *std::max_element(__l.begin(), __l.end()); }

  template<typename _Tp, typename _Compare>
    inline _Tp
    max(initializer_list<_Tp> __l, _Compare __comp)
    { return *std::max_element(__l.begin(), __l.end(), __comp); }

  template<typename _Tp>
    inline pair<_Tp, _Tp>
    minmax(initializer_list<_Tp> __l)
    {
      pair<const _Tp*, const _Tp*> __p =
	std::minmax_element(__l.begin(), __l.end());
      return std::make_pair(*__p.first, *__p.second);
    }

  template<typename _Tp, typename _Compare>
    inline pair<_Tp, _Tp>
    minmax(initializer_list<_Tp> __l, _Compare __comp)
    {
      pair<const _Tp*, const _Tp*> __p =
	std::minmax_element(__l.begin(), __l.end(), __comp);
      return std::make_pair(*__p.first, *__p.second);
    }

  /**
   *  @brief  Checks whether a permutaion of the second sequence is equal
   *          to the first sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @return true if there exists a permutation of the elements in the range
   *          [__first2, __first2 + (__last1 - __first1)), beginning with 
   *          ForwardIterator2 begin, such that equal(__first1, __last1, begin)
   *          returns true; otherwise, returns false.
  */
  template<typename _ForwardIterator1, typename _ForwardIterator2>
    bool
    is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
		   _ForwardIterator2 __first2)
    {
      // Efficiently compare identical prefixes:  O(N) if sequences
      // have the same elements in the same order.
      for (; __first1 != __last1; ++__first1, ++__first2)
	if (!(*__first1 == *__first2))
	  break;

      if (__first1 == __last1)
	return true;

      // Establish __last2 assuming equal ranges by iterating over the
      // rest of the list.
      _ForwardIterator2 __last2 = __first2;
      std::advance(__last2, std::distance(__first1, __last1));
      for (_ForwardIterator1 __scan = __first1; __scan != __last1; ++__scan)
	{
	  if (__scan != _GLIBCXX_STD_A::find(__first1, __scan, *__scan))
	    continue; // We've seen this one before.

	  auto __matches = std::count(__first2, __last2, *__scan);
	  if (0 == __matches
	      || std::count(__scan, __last1, *__scan) != __matches)
	    return false;
	}
      return true;
    }

  /**
   *  @brief  Checks whether a permutation of the second sequence is equal
   *          to the first sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @param  __pred    A binary predicate.
   *  @return true if there exists a permutation of the elements in
   *          the range [__first2, __first2 + (__last1 - __first1)),
   *          beginning with ForwardIterator2 begin, such that
   *          equal(__first1, __last1, __begin, __pred) returns true;
   *          otherwise, returns false.
  */
  template<typename _ForwardIterator1, typename _ForwardIterator2,
	   typename _BinaryPredicate>
    bool
    is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
		   _ForwardIterator2 __first2, _BinaryPredicate __pred)
    {
      // Efficiently compare identical prefixes:  O(N) if sequences
      // have the same elements in the same order.
      for (; __first1 != __last1; ++__first1, ++__first2)
	if (!bool(__pred(*__first1, *__first2)))
	  break;

      if (__first1 == __last1)
	return true;

      // Establish __last2 assuming equal ranges by iterating over the
      // rest of the list.
      _ForwardIterator2 __last2 = __first2;
      std::advance(__last2, std::distance(__first1, __last1));
      for (_ForwardIterator1 __scan = __first1; __scan != __last1; ++__scan)
	{
	  using std::placeholders::_1;

	  if (__scan != _GLIBCXX_STD_A::find_if(__first1, __scan,
						std::bind(__pred, _1, *__scan)))
	    continue; // We've seen this one before.
	  
	  auto __matches = std::count_if(__first2, __last2,
					 std::bind(__pred, _1, *__scan));
	  if (0 == __matches
	      || std::count_if(__scan, __last1,
			       std::bind(__pred, _1, *__scan)) != __matches)
	    return false;
	}
      return true;
    }

#if __cplusplus > 201103L
  /**
   *  @brief  Checks whether a permutaion of the second sequence is equal
   *          to the first sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @param  __last2   End of first range.
   *  @return true if there exists a permutation of the elements in the range
   *          [__first2, __last2), beginning with ForwardIterator2 begin,
   *          such that equal(__first1, __last1, begin) returns true;
   *          otherwise, returns false.
  */
  template<typename _ForwardIterator1, typename _ForwardIterator2>
    bool
    is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
		   _ForwardIterator2 __first2, _ForwardIterator2 __last2)
    {
      using _Cat1
	= typename iterator_traits<_ForwardIterator1>::iterator_category;
      using _Cat2
	= typename iterator_traits<_ForwardIterator2>::iterator_category;
      using _It1_is_RA = is_same<_Cat1, random_access_iterator_tag>;
      using _It2_is_RA = is_same<_Cat2, random_access_iterator_tag>;
      if (_It1_is_RA() && _It2_is_RA())
	{
	  auto __d1 = std::distance(__first1, __last1);
	  auto __d2 = std::distance(__first2, __last2);
	  if (__d1 != __d2)
	    return false;
	}

      // Efficiently compare identical prefixes:  O(N) if sequences
      // have the same elements in the same order.
      for (; __first1 != __last1 && __first2 != __last2; ++__first1, ++__first2)
	if (!(*__first1 == *__first2))
	  break;

      if (__first1 == __last1 && __first2 == __last2)
	return true;

      if (std::distance(__first1, __last1) != std::distance(__first2, __last2))
	return false;

      for (auto __scan = __first1; __scan != __last1; ++__scan)
	{
	  if (__scan != _GLIBCXX_STD_A::find(__first1, __scan, *__scan))
	    continue; // We've seen this one before.

	  auto __matches = std::count(__first2, __last2, *__scan);
	  if (0 == __matches
	      || std::count(__scan, __last1, *__scan) != __matches)
	    return false;
	}
      return true;
    }

  /**
   *  @brief  Checks whether a permutation of the second sequence is equal
   *          to the first sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @param  __last2   End of first range.
   *  @param  __pred    A binary predicate.
   *  @return true if there exists a permutation of the elements in the range
   *          [__first2, __last2), beginning with ForwardIterator2 begin,
   *          such that equal(__first1, __last1, __begin, __pred) returns true;
   *          otherwise, returns false.
  */
  template<typename _ForwardIterator1, typename _ForwardIterator2,
	   typename _BinaryPredicate>
    bool
    is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
		   _ForwardIterator2 __first2, _ForwardIterator2 __last2,
		   _BinaryPredicate __pred)
    {
      using _Cat1
	= typename iterator_traits<_ForwardIterator1>::iterator_category;
      using _Cat2
	= typename iterator_traits<_ForwardIterator2>::iterator_category;
      using _It1_is_RA = is_same<_Cat1, random_access_iterator_tag>;
      using _It2_is_RA = is_same<_Cat2, random_access_iterator_tag>;
      constexpr bool __ra_iters = _It1_is_RA() && _It2_is_RA();
      if (__ra_iters)
	{
	  auto __d1 = std::distance(__first1, __last1);
	  auto __d2 = std::distance(__first2, __last2);
	  if (__d1 != __d2)
	    return false;
	}

      // Efficiently compare identical prefixes:  O(N) if sequences
      // have the same elements in the same order.
      for (; __first1 != __last1; ++__first1, ++__first2)
	if (!bool(__pred(*__first1, *__first2)))
	  break;

      if (__ra_iters)
	{
	  if (__first1 == __last1)
	    return true;
	}
      else
	{
	  auto __d1 = std::distance(__first1, __last1);
	  auto __d2 = std::distance(__first2, __last2);
	  if (__d1 == 0 && __d2 == 0)
	    return true;
	  if (__d1 != __d2)
	    return false;
	}

      for (_ForwardIterator1 __scan = __first1; __scan != __last1; ++__scan)
	{
	  using std::placeholders::_1;

	  if (__scan != _GLIBCXX_STD_A::find_if(__first1, __scan,
						std::bind(__pred, _1, *__scan)))
	    continue; // We've seen this one before.

	  auto __matches = std::count_if(__first2, __last2,
					 std::bind(__pred, _1, *__scan));
	  if (0 == __matches
	      || std::count_if(__scan, __last1,
			       std::bind(__pred, _1, *__scan)) != __matches)
	    return false;
	}
      return true;
    }
#endif

#ifdef _GLIBCXX_USE_C99_STDINT_TR1
  /**
   *  @brief Shuffle the elements of a sequence using a uniform random
   *         number generator.
   *  @ingroup mutating_algorithms
   *  @param  __first   A forward iterator.
   *  @param  __last    A forward iterator.
   *  @param  __g       A UniformRandomNumberGenerator (26.5.1.3).
   *  @return  Nothing.
   *
   *  Reorders the elements in the range @p [__first,__last) using @p __g to
   *  provide random numbers.
  */
  template<typename _RandomAccessIterator,
	   typename _UniformRandomNumberGenerator>
    void
    shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last,
	    _UniformRandomNumberGenerator&& __g)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
	    _RandomAccessIterator>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return;

      typedef typename iterator_traits<_RandomAccessIterator>::difference_type
	_DistanceType;

      typedef typename std::make_unsigned<_DistanceType>::type __ud_type;
      typedef typename std::uniform_int_distribution<__ud_type> __distr_type;
      typedef typename __distr_type::param_type __p_type;
      __distr_type __d;

      for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
	std::iter_swap(__i, __first + __d(__g, __p_type(0, __i - __first)));
    }
#endif

#endif // C++11

_GLIBCXX_END_NAMESPACE_VERSION

_GLIBCXX_BEGIN_NAMESPACE_ALGO

  /**
   *  @brief Apply a function to every element of a sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __f      A unary function object.
   *  @return   @p __f (std::move(@p __f) in C++0x).
   *
   *  Applies the function object @p __f to each element in the range
   *  @p [first,last).  @p __f must not modify the order of the sequence.
   *  If @p __f has a return value it is ignored.
  */
  template<typename _InputIterator, typename _Function>
    _Function
    for_each(_InputIterator __first, _InputIterator __last, _Function __f)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_requires_valid_range(__first, __last);
      for (; __first != __last; ++__first)
	__f(*__first);
      return _GLIBCXX_MOVE(__f);
    }

  /**
   *  @brief Find the first occurrence of a value in a sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __val    The value to find.
   *  @return   The first iterator @c i in the range @p [__first,__last)
   *  such that @c *i == @p __val, or @p __last if no such iterator exists.
  */
  template<typename _InputIterator, typename _Tp>
    inline _InputIterator
    find(_InputIterator __first, _InputIterator __last,
	 const _Tp& __val)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_EqualOpConcept<
		typename iterator_traits<_InputIterator>::value_type, _Tp>)
      __glibcxx_requires_valid_range(__first, __last);
      return std::__find(__first, __last, __val,
		         std::__iterator_category(__first));
    }

  /**
   *  @brief Find the first element in a sequence for which a
   *         predicate is true.
   *  @ingroup non_mutating_algorithms
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __pred   A predicate.
   *  @return   The first iterator @c i in the range @p [__first,__last)
   *  such that @p __pred(*i) is true, or @p __last if no such iterator exists.
  */
  template<typename _InputIterator, typename _Predicate>
    inline _InputIterator
    find_if(_InputIterator __first, _InputIterator __last,
	    _Predicate __pred)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	      typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);
      return std::__find_if(__first, __last, __pred,
			    std::__iterator_category(__first));
    }

  /**
   *  @brief  Find element from a set in a sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  Start of range to search.
   *  @param  __last1   End of range to search.
   *  @param  __first2  Start of match candidates.
   *  @param  __last2   End of match candidates.
   *  @return   The first iterator @c i in the range
   *  @p [__first1,__last1) such that @c *i == @p *(i2) such that i2 is an
   *  iterator in [__first2,__last2), or @p __last1 if no such iterator exists.
   *
   *  Searches the range @p [__first1,__last1) for an element that is
   *  equal to some element in the range [__first2,__last2).  If
   *  found, returns an iterator in the range [__first1,__last1),
   *  otherwise returns @p __last1.
  */
  template<typename _InputIterator, typename _ForwardIterator>
    _InputIterator
    find_first_of(_InputIterator __first1, _InputIterator __last1,
		  _ForwardIterator __first2, _ForwardIterator __last2)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_EqualOpConcept<
	    typename iterator_traits<_InputIterator>::value_type,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);

      for (; __first1 != __last1; ++__first1)
	for (_ForwardIterator __iter = __first2; __iter != __last2; ++__iter)
	  if (*__first1 == *__iter)
	    return __first1;
      return __last1;
    }

  /**
   *  @brief  Find element from a set in a sequence using a predicate.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  Start of range to search.
   *  @param  __last1   End of range to search.
   *  @param  __first2  Start of match candidates.
   *  @param  __last2   End of match candidates.
   *  @param  __comp    Predicate to use.
   *  @return   The first iterator @c i in the range
   *  @p [__first1,__last1) such that @c comp(*i, @p *(i2)) is true
   *  and i2 is an iterator in [__first2,__last2), or @p __last1 if no
   *  such iterator exists.
   *

   *  Searches the range @p [__first1,__last1) for an element that is
   *  equal to some element in the range [__first2,__last2).  If
   *  found, returns an iterator in the range [__first1,__last1),
   *  otherwise returns @p __last1.
  */
  template<typename _InputIterator, typename _ForwardIterator,
	   typename _BinaryPredicate>
    _InputIterator
    find_first_of(_InputIterator __first1, _InputIterator __last1,
		  _ForwardIterator __first2, _ForwardIterator __last2,
		  _BinaryPredicate __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
	    typename iterator_traits<_InputIterator>::value_type,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);

      for (; __first1 != __last1; ++__first1)
	for (_ForwardIterator __iter = __first2; __iter != __last2; ++__iter)
	  if (__comp(*__first1, *__iter))
	    return __first1;
      return __last1;
    }

  /**
   *  @brief Find two adjacent values in a sequence that are equal.
   *  @ingroup non_mutating_algorithms
   *  @param  __first  A forward iterator.
   *  @param  __last   A forward iterator.
   *  @return   The first iterator @c i such that @c i and @c i+1 are both
   *  valid iterators in @p [__first,__last) and such that @c *i == @c *(i+1),
   *  or @p __last if no such iterator exists.
  */
  template<typename _ForwardIterator>
    _ForwardIterator
    adjacent_find(_ForwardIterator __first, _ForwardIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_EqualityComparableConcept<
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);
      if (__first == __last)
	return __last;
      _ForwardIterator __next = __first;
      while(++__next != __last)
	{
	  if (*__first == *__next)
	    return __first;
	  __first = __next;
	}
      return __last;
    }

  /**
   *  @brief Find two adjacent values in a sequence using a predicate.
   *  @ingroup non_mutating_algorithms
   *  @param  __first         A forward iterator.
   *  @param  __last          A forward iterator.
   *  @param  __binary_pred   A binary predicate.
   *  @return   The first iterator @c i such that @c i and @c i+1 are both
   *  valid iterators in @p [__first,__last) and such that
   *  @p __binary_pred(*i,*(i+1)) is true, or @p __last if no such iterator
   *  exists.
  */
  template<typename _ForwardIterator, typename _BinaryPredicate>
    _ForwardIterator
    adjacent_find(_ForwardIterator __first, _ForwardIterator __last,
		  _BinaryPredicate __binary_pred)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
	    typename iterator_traits<_ForwardIterator>::value_type,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);
      if (__first == __last)
	return __last;
      _ForwardIterator __next = __first;
      while(++__next != __last)
	{
	  if (__binary_pred(*__first, *__next))
	    return __first;
	  __first = __next;
	}
      return __last;
    }

  /**
   *  @brief Count the number of copies of a value in a sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __value  The value to be counted.
   *  @return   The number of iterators @c i in the range @p [__first,__last)
   *  for which @c *i == @p __value
  */
  template<typename _InputIterator, typename _Tp>
    typename iterator_traits<_InputIterator>::difference_type
    count(_InputIterator __first, _InputIterator __last, const _Tp& __value)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_EqualOpConcept<
	typename iterator_traits<_InputIterator>::value_type, _Tp>)
      __glibcxx_requires_valid_range(__first, __last);
      typename iterator_traits<_InputIterator>::difference_type __n = 0;
      for (; __first != __last; ++__first)
	if (*__first == __value)
	  ++__n;
      return __n;
    }

  /**
   *  @brief Count the elements of a sequence for which a predicate is true.
   *  @ingroup non_mutating_algorithms
   *  @param  __first  An input iterator.
   *  @param  __last   An input iterator.
   *  @param  __pred   A predicate.
   *  @return   The number of iterators @c i in the range @p [__first,__last)
   *  for which @p __pred(*i) is true.
  */
  template<typename _InputIterator, typename _Predicate>
    typename iterator_traits<_InputIterator>::difference_type
    count_if(_InputIterator __first, _InputIterator __last, _Predicate __pred)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);
      typename iterator_traits<_InputIterator>::difference_type __n = 0;
      for (; __first != __last; ++__first)
	if (__pred(*__first))
	  ++__n;
      return __n;
    }

  /**
   *  @brief Search a sequence for a matching sub-sequence.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1  A forward iterator.
   *  @param  __last1   A forward iterator.
   *  @param  __first2  A forward iterator.
   *  @param  __last2   A forward iterator.
   *  @return The first iterator @c i in the range @p
   *  [__first1,__last1-(__last2-__first2)) such that @c *(i+N) == @p
   *  *(__first2+N) for each @c N in the range @p
   *  [0,__last2-__first2), or @p __last1 if no such iterator exists.
   *
   *  Searches the range @p [__first1,__last1) for a sub-sequence that
   *  compares equal value-by-value with the sequence given by @p
   *  [__first2,__last2) and returns an iterator to the first element
   *  of the sub-sequence, or @p __last1 if the sub-sequence is not
   *  found.
   *
   *  Because the sub-sequence must lie completely within the range @p
   *  [__first1,__last1) it must start at a position less than @p
   *  __last1-(__last2-__first2) where @p __last2-__first2 is the
   *  length of the sub-sequence.
   *
   *  This means that the returned iterator @c i will be in the range
   *  @p [__first1,__last1-(__last2-__first2))
  */
  template<typename _ForwardIterator1, typename _ForwardIterator2>
    _ForwardIterator1
    search(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
	   _ForwardIterator2 __first2, _ForwardIterator2 __last2)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
      __glibcxx_function_requires(_EqualOpConcept<
	    typename iterator_traits<_ForwardIterator1>::value_type,
	    typename iterator_traits<_ForwardIterator2>::value_type>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);

      // Test for empty ranges
      if (__first1 == __last1 || __first2 == __last2)
	return __first1;

      // Test for a pattern of length 1.
      _ForwardIterator2 __p1(__first2);
      if (++__p1 == __last2)
	return _GLIBCXX_STD_A::find(__first1, __last1, *__first2);

      // General case.
      _ForwardIterator2 __p;
      _ForwardIterator1 __current = __first1;

      for (;;)
	{
	  __first1 = _GLIBCXX_STD_A::find(__first1, __last1, *__first2);
	  if (__first1 == __last1)
	    return __last1;

	  __p = __p1;
	  __current = __first1;
	  if (++__current == __last1)
	    return __last1;

	  while (*__current == *__p)
	    {
	      if (++__p == __last2)
		return __first1;
	      if (++__current == __last1)
		return __last1;
	    }
	  ++__first1;
	}
      return __first1;
    }

  /**
   *  @brief Search a sequence for a matching sub-sequence using a predicate.
   *  @ingroup non_mutating_algorithms
   *  @param  __first1     A forward iterator.
   *  @param  __last1      A forward iterator.
   *  @param  __first2     A forward iterator.
   *  @param  __last2      A forward iterator.
   *  @param  __predicate  A binary predicate.
   *  @return   The first iterator @c i in the range
   *  @p [__first1,__last1-(__last2-__first2)) such that
   *  @p __predicate(*(i+N),*(__first2+N)) is true for each @c N in the range
   *  @p [0,__last2-__first2), or @p __last1 if no such iterator exists.
   *
   *  Searches the range @p [__first1,__last1) for a sub-sequence that
   *  compares equal value-by-value with the sequence given by @p
   *  [__first2,__last2), using @p __predicate to determine equality,
   *  and returns an iterator to the first element of the
   *  sub-sequence, or @p __last1 if no such iterator exists.
   *
   *  @see search(_ForwardIter1, _ForwardIter1, _ForwardIter2, _ForwardIter2)
  */
  template<typename _ForwardIterator1, typename _ForwardIterator2,
	   typename _BinaryPredicate>
    _ForwardIterator1
    search(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
	   _ForwardIterator2 __first2, _ForwardIterator2 __last2,
	   _BinaryPredicate  __predicate)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
	    typename iterator_traits<_ForwardIterator1>::value_type,
	    typename iterator_traits<_ForwardIterator2>::value_type>)
      __glibcxx_requires_valid_range(__first1, __last1);
      __glibcxx_requires_valid_range(__first2, __last2);

      // Test for empty ranges
      if (__first1 == __last1 || __first2 == __last2)
	return __first1;

      // Test for a pattern of length 1.
      _ForwardIterator2 __p1(__first2);
      if (++__p1 == __last2)
	{
	  while (__first1 != __last1
		 && !bool(__predicate(*__first1, *__first2)))
	    ++__first1;
	  return __first1;
	}

      // General case.
      _ForwardIterator2 __p;
      _ForwardIterator1 __current = __first1;

      for (;;)
	{
	  while (__first1 != __last1
		 && !bool(__predicate(*__first1, *__first2)))
	    ++__first1;
	  if (__first1 == __last1)
	    return __last1;

	  __p = __p1;
	  __current = __first1;
	  if (++__current == __last1)
	    return __last1;

	  while (__predicate(*__current, *__p))
	    {
	      if (++__p == __last2)
		return __first1;
	      if (++__current == __last1)
		return __last1;
	    }
	  ++__first1;
	}
      return __first1;
    }


  /**
   *  @brief Search a sequence for a number of consecutive values.
   *  @ingroup non_mutating_algorithms
   *  @param  __first  A forward iterator.
   *  @param  __last   A forward iterator.
   *  @param  __count  The number of consecutive values.
   *  @param  __val    The value to find.
   *  @return The first iterator @c i in the range @p
   *  [__first,__last-__count) such that @c *(i+N) == @p __val for
   *  each @c N in the range @p [0,__count), or @p __last if no such
   *  iterator exists.
   *
   *  Searches the range @p [__first,__last) for @p count consecutive elements
   *  equal to @p __val.
  */
  template<typename _ForwardIterator, typename _Integer, typename _Tp>
    _ForwardIterator
    search_n(_ForwardIterator __first, _ForwardIterator __last,
	     _Integer __count, const _Tp& __val)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_EqualOpConcept<
	typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__count <= 0)
	return __first;
      if (__count == 1)
	return _GLIBCXX_STD_A::find(__first, __last, __val);
      return std::__search_n(__first, __last, __count, __val,
			     std::__iterator_category(__first));
    }


  /**
   *  @brief Search a sequence for a number of consecutive values using a
   *         predicate.
   *  @ingroup non_mutating_algorithms
   *  @param  __first        A forward iterator.
   *  @param  __last         A forward iterator.
   *  @param  __count        The number of consecutive values.
   *  @param  __val          The value to find.
   *  @param  __binary_pred  A binary predicate.
   *  @return The first iterator @c i in the range @p
   *  [__first,__last-__count) such that @p
   *  __binary_pred(*(i+N),__val) is true for each @c N in the range
   *  @p [0,__count), or @p __last if no such iterator exists.
   *
   *  Searches the range @p [__first,__last) for @p __count
   *  consecutive elements for which the predicate returns true.
  */
  template<typename _ForwardIterator, typename _Integer, typename _Tp,
           typename _BinaryPredicate>
    _ForwardIterator
    search_n(_ForwardIterator __first, _ForwardIterator __last,
	     _Integer __count, const _Tp& __val,
	     _BinaryPredicate __binary_pred)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
	    typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__count <= 0)
	return __first;
      if (__count == 1)
	{
	  while (__first != __last && !bool(__binary_pred(*__first, __val)))
	    ++__first;
	  return __first;
	}
      return std::__search_n(__first, __last, __count, __val, __binary_pred,
			     std::__iterator_category(__first));
    }


  /**
   *  @brief Perform an operation on a sequence.
   *  @ingroup mutating_algorithms
   *  @param  __first     An input iterator.
   *  @param  __last      An input iterator.
   *  @param  __result    An output iterator.
   *  @param  __unary_op  A unary operator.
   *  @return   An output iterator equal to @p __result+(__last-__first).
   *
   *  Applies the operator to each element in the input range and assigns
   *  the results to successive elements of the output sequence.
   *  Evaluates @p *(__result+N)=unary_op(*(__first+N)) for each @c N in the
   *  range @p [0,__last-__first).
   *
   *  @p unary_op must not alter its argument.
  */
  template<typename _InputIterator, typename _OutputIterator,
	   typename _UnaryOperation>
    _OutputIterator
    transform(_InputIterator __first, _InputIterator __last,
	      _OutputIterator __result, _UnaryOperation __unary_op)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
            // "the type returned by a _UnaryOperation"
            __typeof__(__unary_op(*__first))>)
      __glibcxx_requires_valid_range(__first, __last);

      for (; __first != __last; ++__first, ++__result)
	*__result = __unary_op(*__first);
      return __result;
    }

  /**
   *  @brief Perform an operation on corresponding elements of two sequences.
   *  @ingroup mutating_algorithms
   *  @param  __first1     An input iterator.
   *  @param  __last1      An input iterator.
   *  @param  __first2     An input iterator.
   *  @param  __result     An output iterator.
   *  @param  __binary_op  A binary operator.
   *  @return   An output iterator equal to @p result+(last-first).
   *
   *  Applies the operator to the corresponding elements in the two
   *  input ranges and assigns the results to successive elements of the
   *  output sequence.
   *  Evaluates @p
   *  *(__result+N)=__binary_op(*(__first1+N),*(__first2+N)) for each
   *  @c N in the range @p [0,__last1-__first1).
   *
   *  @p binary_op must not alter either of its arguments.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator, typename _BinaryOperation>
    _OutputIterator
    transform(_InputIterator1 __first1, _InputIterator1 __last1,
	      _InputIterator2 __first2, _OutputIterator __result,
	      _BinaryOperation __binary_op)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
            // "the type returned by a _BinaryOperation"
            __typeof__(__binary_op(*__first1,*__first2))>)
      __glibcxx_requires_valid_range(__first1, __last1);

      for (; __first1 != __last1; ++__first1, ++__first2, ++__result)
	*__result = __binary_op(*__first1, *__first2);
      return __result;
    }

  /**
   *  @brief Replace each occurrence of one value in a sequence with another
   *         value.
   *  @ingroup mutating_algorithms
   *  @param  __first      A forward iterator.
   *  @param  __last       A forward iterator.
   *  @param  __old_value  The value to be replaced.
   *  @param  __new_value  The replacement value.
   *  @return   replace() returns no value.
   *
   *  For each iterator @c i in the range @p [__first,__last) if @c *i ==
   *  @p __old_value then the assignment @c *i = @p __new_value is performed.
  */
  template<typename _ForwardIterator, typename _Tp>
    void
    replace(_ForwardIterator __first, _ForwardIterator __last,
	    const _Tp& __old_value, const _Tp& __new_value)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator>)
      __glibcxx_function_requires(_EqualOpConcept<
	    typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
      __glibcxx_function_requires(_ConvertibleConcept<_Tp,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      for (; __first != __last; ++__first)
	if (*__first == __old_value)
	  *__first = __new_value;
    }

  /**
   *  @brief Replace each value in a sequence for which a predicate returns
   *         true with another value.
   *  @ingroup mutating_algorithms
   *  @param  __first      A forward iterator.
   *  @param  __last       A forward iterator.
   *  @param  __pred       A predicate.
   *  @param  __new_value  The replacement value.
   *  @return   replace_if() returns no value.
   *
   *  For each iterator @c i in the range @p [__first,__last) if @p __pred(*i)
   *  is true then the assignment @c *i = @p __new_value is performed.
  */
  template<typename _ForwardIterator, typename _Predicate, typename _Tp>
    void
    replace_if(_ForwardIterator __first, _ForwardIterator __last,
	       _Predicate __pred, const _Tp& __new_value)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator>)
      __glibcxx_function_requires(_ConvertibleConcept<_Tp,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      for (; __first != __last; ++__first)
	if (__pred(*__first))
	  *__first = __new_value;
    }

  /**
   *  @brief Assign the result of a function object to each value in a
   *         sequence.
   *  @ingroup mutating_algorithms
   *  @param  __first  A forward iterator.
   *  @param  __last   A forward iterator.
   *  @param  __gen    A function object taking no arguments and returning
   *                 std::iterator_traits<_ForwardIterator>::value_type
   *  @return   generate() returns no value.
   *
   *  Performs the assignment @c *i = @p __gen() for each @c i in the range
   *  @p [__first,__last).
  */
  template<typename _ForwardIterator, typename _Generator>
    void
    generate(_ForwardIterator __first, _ForwardIterator __last,
	     _Generator __gen)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_GeneratorConcept<_Generator,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      for (; __first != __last; ++__first)
	*__first = __gen();
    }

  /**
   *  @brief Assign the result of a function object to each value in a
   *         sequence.
   *  @ingroup mutating_algorithms
   *  @param  __first  A forward iterator.
   *  @param  __n      The length of the sequence.
   *  @param  __gen    A function object taking no arguments and returning
   *                 std::iterator_traits<_ForwardIterator>::value_type
   *  @return   The end of the sequence, @p __first+__n
   *
   *  Performs the assignment @c *i = @p __gen() for each @c i in the range
   *  @p [__first,__first+__n).
   *
   *  _GLIBCXX_RESOLVE_LIB_DEFECTS
   *  DR 865. More algorithms that throw away information
  */
  template<typename _OutputIterator, typename _Size, typename _Generator>
    _OutputIterator
    generate_n(_OutputIterator __first, _Size __n, _Generator __gen)
    {
      // concept requirements
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
            // "the type returned by a _Generator"
            __typeof__(__gen())>)

      for (__decltype(__n + 0) __niter = __n;
	   __niter > 0; --__niter, ++__first)
	*__first = __gen();
      return __first;
    }


  /**
   *  @brief Copy a sequence, removing consecutive duplicate values.
   *  @ingroup mutating_algorithms
   *  @param  __first   An input iterator.
   *  @param  __last    An input iterator.
   *  @param  __result  An output iterator.
   *  @return   An iterator designating the end of the resulting sequence.
   *
   *  Copies each element in the range @p [__first,__last) to the range
   *  beginning at @p __result, except that only the first element is copied
   *  from groups of consecutive elements that compare equal.
   *  unique_copy() is stable, so the relative order of elements that are
   *  copied is unchanged.
   *
   *  _GLIBCXX_RESOLVE_LIB_DEFECTS
   *  DR 241. Does unique_copy() require CopyConstructible and Assignable?
   *  
   *  _GLIBCXX_RESOLVE_LIB_DEFECTS
   *  DR 538. 241 again: Does unique_copy() require CopyConstructible and 
   *  Assignable?
  */
  template<typename _InputIterator, typename _OutputIterator>
    inline _OutputIterator
    unique_copy(_InputIterator __first, _InputIterator __last,
		_OutputIterator __result)
    {
      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_function_requires(_EqualityComparableConcept<
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return __result;
      return std::__unique_copy(__first, __last, __result,
				std::__iterator_category(__first),
				std::__iterator_category(__result));
    }

  /**
   *  @brief Copy a sequence, removing consecutive values using a predicate.
   *  @ingroup mutating_algorithms
   *  @param  __first        An input iterator.
   *  @param  __last         An input iterator.
   *  @param  __result       An output iterator.
   *  @param  __binary_pred  A binary predicate.
   *  @return   An iterator designating the end of the resulting sequence.
   *
   *  Copies each element in the range @p [__first,__last) to the range
   *  beginning at @p __result, except that only the first element is copied
   *  from groups of consecutive elements for which @p __binary_pred returns
   *  true.
   *  unique_copy() is stable, so the relative order of elements that are
   *  copied is unchanged.
   *
   *  _GLIBCXX_RESOLVE_LIB_DEFECTS
   *  DR 241. Does unique_copy() require CopyConstructible and Assignable?
  */
  template<typename _InputIterator, typename _OutputIterator,
	   typename _BinaryPredicate>
    inline _OutputIterator
    unique_copy(_InputIterator __first, _InputIterator __last,
		_OutputIterator __result,
		_BinaryPredicate __binary_pred)
    {
      // concept requirements -- predicates checked later
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
	    typename iterator_traits<_InputIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return __result;
      return std::__unique_copy(__first, __last, __result, __binary_pred,
				std::__iterator_category(__first),
				std::__iterator_category(__result));
    }


  /**
   *  @brief Randomly shuffle the elements of a sequence.
   *  @ingroup mutating_algorithms
   *  @param  __first   A forward iterator.
   *  @param  __last    A forward iterator.
   *  @return  Nothing.
   *
   *  Reorder the elements in the range @p [__first,__last) using a random
   *  distribution, so that every possible ordering of the sequence is
   *  equally likely.
  */
  template<typename _RandomAccessIterator>
    inline void
    random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
	    _RandomAccessIterator>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first != __last)
	for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
	  std::iter_swap(__i, __first + (std::rand() % ((__i - __first) + 1)));
    }

  /**
   *  @brief Shuffle the elements of a sequence using a random number
   *         generator.
   *  @ingroup mutating_algorithms
   *  @param  __first   A forward iterator.
   *  @param  __last    A forward iterator.
   *  @param  __rand    The RNG functor or function.
   *  @return  Nothing.
   *
   *  Reorders the elements in the range @p [__first,__last) using @p __rand to
   *  provide a random distribution. Calling @p __rand(N) for a positive
   *  integer @p N should return a randomly chosen integer from the
   *  range [0,N).
  */
  template<typename _RandomAccessIterator, typename _RandomNumberGenerator>
    void
    random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last,
#if __cplusplus >= 201103L
		   _RandomNumberGenerator&& __rand)
#else
		   _RandomNumberGenerator& __rand)
#endif
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
	    _RandomAccessIterator>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return;
      for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
	std::iter_swap(__i, __first + __rand((__i - __first) + 1));
    }


  /**
   *  @brief Move elements for which a predicate is true to the beginning
   *         of a sequence.
   *  @ingroup mutating_algorithms
   *  @param  __first   A forward iterator.
   *  @param  __last    A forward iterator.
   *  @param  __pred    A predicate functor.
   *  @return  An iterator @p middle such that @p __pred(i) is true for each
   *  iterator @p i in the range @p [__first,middle) and false for each @p i
   *  in the range @p [middle,__last).
   *
   *  @p __pred must not modify its operand. @p partition() does not preserve
   *  the relative ordering of elements in each group, use
   *  @p stable_partition() if this is needed.
  */
  template<typename _ForwardIterator, typename _Predicate>
    inline _ForwardIterator
    partition(_ForwardIterator __first, _ForwardIterator __last,
	      _Predicate   __pred)
    {
      // concept requirements
      __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
				  _ForwardIterator>)
      __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      return std::__partition(__first, __last, __pred,
			      std::__iterator_category(__first));
    }



  /**
   *  @brief Sort the smallest elements of a sequence.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __middle  Another iterator.
   *  @param  __last    Another iterator.
   *  @return  Nothing.
   *
   *  Sorts the smallest @p (__middle-__first) elements in the range
   *  @p [first,last) and moves them to the range @p [__first,__middle). The
   *  order of the remaining elements in the range @p [__middle,__last) is
   *  undefined.
   *  After the sort if @e i and @e j are iterators in the range
   *  @p [__first,__middle) such that i precedes j and @e k is an iterator in
   *  the range @p [__middle,__last) then *j<*i and *k<*i are both false.
  */
  template<typename _RandomAccessIterator>
    inline void
    partial_sort(_RandomAccessIterator __first,
		 _RandomAccessIterator __middle,
		 _RandomAccessIterator __last)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;

      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
	    _RandomAccessIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<_ValueType>)
      __glibcxx_requires_valid_range(__first, __middle);
      __glibcxx_requires_valid_range(__middle, __last);

      std::__heap_select(__first, __middle, __last);
      std::sort_heap(__first, __middle);
    }

  /**
   *  @brief Sort the smallest elements of a sequence using a predicate
   *         for comparison.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __middle  Another iterator.
   *  @param  __last    Another iterator.
   *  @param  __comp    A comparison functor.
   *  @return  Nothing.
   *
   *  Sorts the smallest @p (__middle-__first) elements in the range
   *  @p [__first,__last) and moves them to the range @p [__first,__middle). The
   *  order of the remaining elements in the range @p [__middle,__last) is
   *  undefined.
   *  After the sort if @e i and @e j are iterators in the range
   *  @p [__first,__middle) such that i precedes j and @e k is an iterator in
   *  the range @p [__middle,__last) then @p *__comp(j,*i) and @p __comp(*k,*i)
   *  are both false.
  */
  template<typename _RandomAccessIterator, typename _Compare>
    inline void
    partial_sort(_RandomAccessIterator __first,
		 _RandomAccessIterator __middle,
		 _RandomAccessIterator __last,
		 _Compare __comp)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;

      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
	    _RandomAccessIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType, _ValueType>)
      __glibcxx_requires_valid_range(__first, __middle);
      __glibcxx_requires_valid_range(__middle, __last);

      std::__heap_select(__first, __middle, __last, __comp);
      std::sort_heap(__first, __middle, __comp);
    }

  /**
   *  @brief Sort a sequence just enough to find a particular position.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __nth     Another iterator.
   *  @param  __last    Another iterator.
   *  @return  Nothing.
   *
   *  Rearranges the elements in the range @p [__first,__last) so that @p *__nth
   *  is the same element that would have been in that position had the
   *  whole sequence been sorted. The elements either side of @p *__nth are
   *  not completely sorted, but for any iterator @e i in the range
   *  @p [__first,__nth) and any iterator @e j in the range @p [__nth,__last) it
   *  holds that *j < *i is false.
  */
  template<typename _RandomAccessIterator>
    inline void
    nth_element(_RandomAccessIterator __first, _RandomAccessIterator __nth,
		_RandomAccessIterator __last)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;

      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
				  _RandomAccessIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<_ValueType>)
      __glibcxx_requires_valid_range(__first, __nth);
      __glibcxx_requires_valid_range(__nth, __last);

      if (__first == __last || __nth == __last)
	return;

      std::__introselect(__first, __nth, __last,
			 std::__lg(__last - __first) * 2);
    }

  /**
   *  @brief Sort a sequence just enough to find a particular position
   *         using a predicate for comparison.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __nth     Another iterator.
   *  @param  __last    Another iterator.
   *  @param  __comp    A comparison functor.
   *  @return  Nothing.
   *
   *  Rearranges the elements in the range @p [__first,__last) so that @p *__nth
   *  is the same element that would have been in that position had the
   *  whole sequence been sorted. The elements either side of @p *__nth are
   *  not completely sorted, but for any iterator @e i in the range
   *  @p [__first,__nth) and any iterator @e j in the range @p [__nth,__last) it
   *  holds that @p __comp(*j,*i) is false.
  */
  template<typename _RandomAccessIterator, typename _Compare>
    inline void
    nth_element(_RandomAccessIterator __first, _RandomAccessIterator __nth,
		_RandomAccessIterator __last, _Compare __comp)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;

      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
				  _RandomAccessIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType, _ValueType>)
      __glibcxx_requires_valid_range(__first, __nth);
      __glibcxx_requires_valid_range(__nth, __last);

      if (__first == __last || __nth == __last)
	return;

      std::__introselect(__first, __nth, __last,
			 std::__lg(__last - __first) * 2, __comp);
    }


  /**
   *  @brief Sort the elements of a sequence.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @return  Nothing.
   *
   *  Sorts the elements in the range @p [__first,__last) in ascending order,
   *  such that for each iterator @e i in the range @p [__first,__last-1),  
   *  *(i+1)<*i is false.
   *
   *  The relative ordering of equivalent elements is not preserved, use
   *  @p stable_sort() if this is needed.
  */
  template<typename _RandomAccessIterator>
    inline void
    sort(_RandomAccessIterator __first, _RandomAccessIterator __last)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;

      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
	    _RandomAccessIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<_ValueType>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first != __last)
	{
	  std::__introsort_loop(__first, __last,
				std::__lg(__last - __first) * 2);
	  std::__final_insertion_sort(__first, __last);
	}
    }

  /**
   *  @brief Sort the elements of a sequence using a predicate for comparison.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __comp    A comparison functor.
   *  @return  Nothing.
   *
   *  Sorts the elements in the range @p [__first,__last) in ascending order,
   *  such that @p __comp(*(i+1),*i) is false for every iterator @e i in the
   *  range @p [__first,__last-1).
   *
   *  The relative ordering of equivalent elements is not preserved, use
   *  @p stable_sort() if this is needed.
  */
  template<typename _RandomAccessIterator, typename _Compare>
    inline void
    sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
	 _Compare __comp)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;

      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
	    _RandomAccessIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare, _ValueType,
				  _ValueType>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first != __last)
	{
	  std::__introsort_loop(__first, __last,
				std::__lg(__last - __first) * 2, __comp);
	  std::__final_insertion_sort(__first, __last, __comp);
	}
    }

  /**
   *  @brief Merges two sorted ranges.
   *  @ingroup sorting_algorithms
   *  @param  __first1  An iterator.
   *  @param  __first2  Another iterator.
   *  @param  __last1   Another iterator.
   *  @param  __last2   Another iterator.
   *  @param  __result  An iterator pointing to the end of the merged range.
   *  @return         An iterator pointing to the first element <em>not less
   *                  than</em> @e val.
   *
   *  Merges the ranges @p [__first1,__last1) and @p [__first2,__last2) into
   *  the sorted range @p [__result, __result + (__last1-__first1) +
   *  (__last2-__first2)).  Both input ranges must be sorted, and the
   *  output range must not overlap with either of the input ranges.
   *  The sort is @e stable, that is, for equivalent elements in the
   *  two ranges, elements from the first range will always come
   *  before elements from the second.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator>
    _OutputIterator
    merge(_InputIterator1 __first1, _InputIterator1 __last1,
	  _InputIterator2 __first2, _InputIterator2 __last2,
	  _OutputIterator __result)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType1>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType2>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType2, _ValueType1>)	
      __glibcxx_requires_sorted_set(__first1, __last1, __first2);
      __glibcxx_requires_sorted_set(__first2, __last2, __first1);

      while (__first1 != __last1 && __first2 != __last2)
	{
	  if (*__first2 < *__first1)
	    {
	      *__result = *__first2;
	      ++__first2;
	    }
	  else
	    {
	      *__result = *__first1;
	      ++__first1;
	    }
	  ++__result;
	}
      return std::copy(__first2, __last2, std::copy(__first1, __last1,
						    __result));
    }

  /**
   *  @brief Merges two sorted ranges.
   *  @ingroup sorting_algorithms
   *  @param  __first1  An iterator.
   *  @param  __first2  Another iterator.
   *  @param  __last1   Another iterator.
   *  @param  __last2   Another iterator.
   *  @param  __result  An iterator pointing to the end of the merged range.
   *  @param  __comp    A functor to use for comparisons.
   *  @return         An iterator pointing to the first element "not less
   *                  than" @e val.
   *
   *  Merges the ranges @p [__first1,__last1) and @p [__first2,__last2) into
   *  the sorted range @p [__result, __result + (__last1-__first1) +
   *  (__last2-__first2)).  Both input ranges must be sorted, and the
   *  output range must not overlap with either of the input ranges.
   *  The sort is @e stable, that is, for equivalent elements in the
   *  two ranges, elements from the first range will always come
   *  before elements from the second.
   *
   *  The comparison function should have the same effects on ordering as
   *  the function used for the initial sort.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator, typename _Compare>
    _OutputIterator
    merge(_InputIterator1 __first1, _InputIterator1 __last1,
	  _InputIterator2 __first2, _InputIterator2 __last2,
	  _OutputIterator __result, _Compare __comp)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType1>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType2>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType2, _ValueType1>)
      __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
      __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);

      while (__first1 != __last1 && __first2 != __last2)
	{
	  if (__comp(*__first2, *__first1))
	    {
	      *__result = *__first2;
	      ++__first2;
	    }
	  else
	    {
	      *__result = *__first1;
	      ++__first1;
	    }
	  ++__result;
	}
      return std::copy(__first2, __last2, std::copy(__first1, __last1,
						    __result));
    }


  /**
   *  @brief Sort the elements of a sequence, preserving the relative order
   *         of equivalent elements.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @return  Nothing.
   *
   *  Sorts the elements in the range @p [__first,__last) in ascending order,
   *  such that for each iterator @p i in the range @p [__first,__last-1),
   *  @p *(i+1)<*i is false.
   *
   *  The relative ordering of equivalent elements is preserved, so any two
   *  elements @p x and @p y in the range @p [__first,__last) such that
   *  @p x<y is false and @p y<x is false will have the same relative
   *  ordering after calling @p stable_sort().
  */
  template<typename _RandomAccessIterator>
    inline void
    stable_sort(_RandomAccessIterator __first, _RandomAccessIterator __last)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;
      typedef typename iterator_traits<_RandomAccessIterator>::difference_type
	_DistanceType;

      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
	    _RandomAccessIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<_ValueType>)
      __glibcxx_requires_valid_range(__first, __last);

      _Temporary_buffer<_RandomAccessIterator, _ValueType> __buf(__first,
								 __last);
      if (__buf.begin() == 0)
	std::__inplace_stable_sort(__first, __last);
      else
	std::__stable_sort_adaptive(__first, __last, __buf.begin(),
				    _DistanceType(__buf.size()));
    }

  /**
   *  @brief Sort the elements of a sequence using a predicate for comparison,
   *         preserving the relative order of equivalent elements.
   *  @ingroup sorting_algorithms
   *  @param  __first   An iterator.
   *  @param  __last    Another iterator.
   *  @param  __comp    A comparison functor.
   *  @return  Nothing.
   *
   *  Sorts the elements in the range @p [__first,__last) in ascending order,
   *  such that for each iterator @p i in the range @p [__first,__last-1),
   *  @p __comp(*(i+1),*i) is false.
   *
   *  The relative ordering of equivalent elements is preserved, so any two
   *  elements @p x and @p y in the range @p [__first,__last) such that
   *  @p __comp(x,y) is false and @p __comp(y,x) is false will have the same
   *  relative ordering after calling @p stable_sort().
  */
  template<typename _RandomAccessIterator, typename _Compare>
    inline void
    stable_sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
		_Compare __comp)
    {
      typedef typename iterator_traits<_RandomAccessIterator>::value_type
	_ValueType;
      typedef typename iterator_traits<_RandomAccessIterator>::difference_type
	_DistanceType;

      // concept requirements
      __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
	    _RandomAccessIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType,
				  _ValueType>)
      __glibcxx_requires_valid_range(__first, __last);

      _Temporary_buffer<_RandomAccessIterator, _ValueType> __buf(__first,
								 __last);
      if (__buf.begin() == 0)
	std::__inplace_stable_sort(__first, __last, __comp);
      else
	std::__stable_sort_adaptive(__first, __last, __buf.begin(),
				    _DistanceType(__buf.size()), __comp);
    }


  /**
   *  @brief Return the union of two sorted ranges.
   *  @ingroup set_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @param  __last2   End of second range.
   *  @return  End of the output range.
   *  @ingroup set_algorithms
   *
   *  This operation iterates over both ranges, copying elements present in
   *  each range in order to the output range.  Iterators increment for each
   *  range.  When the current element of one range is less than the other,
   *  that element is copied and the iterator advanced.  If an element is
   *  contained in both ranges, the element from the first range is copied and
   *  both ranges advance.  The output range may not overlap either input
   *  range.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator>
    _OutputIterator
    set_union(_InputIterator1 __first1, _InputIterator1 __last1,
	      _InputIterator2 __first2, _InputIterator2 __last2,
	      _OutputIterator __result)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType1>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType2>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType1, _ValueType2>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType2, _ValueType1>)
      __glibcxx_requires_sorted_set(__first1, __last1, __first2);
      __glibcxx_requires_sorted_set(__first2, __last2, __first1);

      while (__first1 != __last1 && __first2 != __last2)
	{
	  if (*__first1 < *__first2)
	    {
	      *__result = *__first1;
	      ++__first1;
	    }
	  else if (*__first2 < *__first1)
	    {
	      *__result = *__first2;
	      ++__first2;
	    }
	  else
	    {
	      *__result = *__first1;
	      ++__first1;
	      ++__first2;
	    }
	  ++__result;
	}
      return std::copy(__first2, __last2, std::copy(__first1, __last1,
						    __result));
    }

  /**
   *  @brief Return the union of two sorted ranges using a comparison functor.
   *  @ingroup set_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @param  __last2   End of second range.
   *  @param  __comp    The comparison functor.
   *  @return  End of the output range.
   *  @ingroup set_algorithms
   *
   *  This operation iterates over both ranges, copying elements present in
   *  each range in order to the output range.  Iterators increment for each
   *  range.  When the current element of one range is less than the other
   *  according to @p __comp, that element is copied and the iterator advanced.
   *  If an equivalent element according to @p __comp is contained in both
   *  ranges, the element from the first range is copied and both ranges
   *  advance.  The output range may not overlap either input range.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator, typename _Compare>
    _OutputIterator
    set_union(_InputIterator1 __first1, _InputIterator1 __last1,
	      _InputIterator2 __first2, _InputIterator2 __last2,
	      _OutputIterator __result, _Compare __comp)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType1>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType2>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType1, _ValueType2>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType2, _ValueType1>)
      __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
      __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);

      while (__first1 != __last1 && __first2 != __last2)
	{
	  if (__comp(*__first1, *__first2))
	    {
	      *__result = *__first1;
	      ++__first1;
	    }
	  else if (__comp(*__first2, *__first1))
	    {
	      *__result = *__first2;
	      ++__first2;
	    }
	  else
	    {
	      *__result = *__first1;
	      ++__first1;
	      ++__first2;
	    }
	  ++__result;
	}
      return std::copy(__first2, __last2, std::copy(__first1, __last1,
						    __result));
    }

  /**
   *  @brief Return the intersection of two sorted ranges.
   *  @ingroup set_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @param  __last2   End of second range.
   *  @return  End of the output range.
   *  @ingroup set_algorithms
   *
   *  This operation iterates over both ranges, copying elements present in
   *  both ranges in order to the output range.  Iterators increment for each
   *  range.  When the current element of one range is less than the other,
   *  that iterator advances.  If an element is contained in both ranges, the
   *  element from the first range is copied and both ranges advance.  The
   *  output range may not overlap either input range.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator>
    _OutputIterator
    set_intersection(_InputIterator1 __first1, _InputIterator1 __last1,
		     _InputIterator2 __first2, _InputIterator2 __last2,
		     _OutputIterator __result)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType1>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType1, _ValueType2>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType2, _ValueType1>)
      __glibcxx_requires_sorted_set(__first1, __last1, __first2);
      __glibcxx_requires_sorted_set(__first2, __last2, __first1);

      while (__first1 != __last1 && __first2 != __last2)
	if (*__first1 < *__first2)
	  ++__first1;
	else if (*__first2 < *__first1)
	  ++__first2;
	else
	  {
	    *__result = *__first1;
	    ++__first1;
	    ++__first2;
	    ++__result;
	  }
      return __result;
    }

  /**
   *  @brief Return the intersection of two sorted ranges using comparison
   *  functor.
   *  @ingroup set_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @param  __last2   End of second range.
   *  @param  __comp    The comparison functor.
   *  @return  End of the output range.
   *  @ingroup set_algorithms
   *
   *  This operation iterates over both ranges, copying elements present in
   *  both ranges in order to the output range.  Iterators increment for each
   *  range.  When the current element of one range is less than the other
   *  according to @p __comp, that iterator advances.  If an element is
   *  contained in both ranges according to @p __comp, the element from the
   *  first range is copied and both ranges advance.  The output range may not
   *  overlap either input range.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator, typename _Compare>
    _OutputIterator
    set_intersection(_InputIterator1 __first1, _InputIterator1 __last1,
		     _InputIterator2 __first2, _InputIterator2 __last2,
		     _OutputIterator __result, _Compare __comp)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType1>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType1, _ValueType2>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType2, _ValueType1>)
      __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
      __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);

      while (__first1 != __last1 && __first2 != __last2)
	if (__comp(*__first1, *__first2))
	  ++__first1;
	else if (__comp(*__first2, *__first1))
	  ++__first2;
	else
	  {
	    *__result = *__first1;
	    ++__first1;
	    ++__first2;
	    ++__result;
	  }
      return __result;
    }

  /**
   *  @brief Return the difference of two sorted ranges.
   *  @ingroup set_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @param  __last2   End of second range.
   *  @return  End of the output range.
   *  @ingroup set_algorithms
   *
   *  This operation iterates over both ranges, copying elements present in
   *  the first range but not the second in order to the output range.
   *  Iterators increment for each range.  When the current element of the
   *  first range is less than the second, that element is copied and the
   *  iterator advances.  If the current element of the second range is less,
   *  the iterator advances, but no element is copied.  If an element is
   *  contained in both ranges, no elements are copied and both ranges
   *  advance.  The output range may not overlap either input range.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator>
    _OutputIterator
    set_difference(_InputIterator1 __first1, _InputIterator1 __last1,
		   _InputIterator2 __first2, _InputIterator2 __last2,
		   _OutputIterator __result)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType1>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType1, _ValueType2>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType2, _ValueType1>)	
      __glibcxx_requires_sorted_set(__first1, __last1, __first2);
      __glibcxx_requires_sorted_set(__first2, __last2, __first1);

      while (__first1 != __last1 && __first2 != __last2)
	if (*__first1 < *__first2)
	  {
	    *__result = *__first1;
	    ++__first1;
	    ++__result;
	  }
	else if (*__first2 < *__first1)
	  ++__first2;
	else
	  {
	    ++__first1;
	    ++__first2;
	  }
      return std::copy(__first1, __last1, __result);
    }

  /**
   *  @brief  Return the difference of two sorted ranges using comparison
   *  functor.
   *  @ingroup set_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @param  __last2   End of second range.
   *  @param  __comp    The comparison functor.
   *  @return  End of the output range.
   *  @ingroup set_algorithms
   *
   *  This operation iterates over both ranges, copying elements present in
   *  the first range but not the second in order to the output range.
   *  Iterators increment for each range.  When the current element of the
   *  first range is less than the second according to @p __comp, that element
   *  is copied and the iterator advances.  If the current element of the
   *  second range is less, no element is copied and the iterator advances.
   *  If an element is contained in both ranges according to @p __comp, no
   *  elements are copied and both ranges advance.  The output range may not
   *  overlap either input range.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator, typename _Compare>
    _OutputIterator
    set_difference(_InputIterator1 __first1, _InputIterator1 __last1,
		   _InputIterator2 __first2, _InputIterator2 __last2,
		   _OutputIterator __result, _Compare __comp)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType1>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType1, _ValueType2>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType2, _ValueType1>)
      __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
      __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);

      while (__first1 != __last1 && __first2 != __last2)
	if (__comp(*__first1, *__first2))
	  {
	    *__result = *__first1;
	    ++__first1;
	    ++__result;
	  }
	else if (__comp(*__first2, *__first1))
	  ++__first2;
	else
	  {
	    ++__first1;
	    ++__first2;
	  }
      return std::copy(__first1, __last1, __result);
    }

  /**
   *  @brief  Return the symmetric difference of two sorted ranges.
   *  @ingroup set_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @param  __last2   End of second range.
   *  @return  End of the output range.
   *  @ingroup set_algorithms
   *
   *  This operation iterates over both ranges, copying elements present in
   *  one range but not the other in order to the output range.  Iterators
   *  increment for each range.  When the current element of one range is less
   *  than the other, that element is copied and the iterator advances.  If an
   *  element is contained in both ranges, no elements are copied and both
   *  ranges advance.  The output range may not overlap either input range.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator>
    _OutputIterator
    set_symmetric_difference(_InputIterator1 __first1, _InputIterator1 __last1,
			     _InputIterator2 __first2, _InputIterator2 __last2,
			     _OutputIterator __result)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType1>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType2>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType1, _ValueType2>)
      __glibcxx_function_requires(_LessThanOpConcept<_ValueType2, _ValueType1>)	
      __glibcxx_requires_sorted_set(__first1, __last1, __first2);
      __glibcxx_requires_sorted_set(__first2, __last2, __first1);

      while (__first1 != __last1 && __first2 != __last2)
	if (*__first1 < *__first2)
	  {
	    *__result = *__first1;
	    ++__first1;
	    ++__result;
	  }
	else if (*__first2 < *__first1)
	  {
	    *__result = *__first2;
	    ++__first2;
	    ++__result;
	  }
	else
	  {
	    ++__first1;
	    ++__first2;
	  }
      return std::copy(__first2, __last2, std::copy(__first1,
						    __last1, __result));
    }

  /**
   *  @brief  Return the symmetric difference of two sorted ranges using
   *  comparison functor.
   *  @ingroup set_algorithms
   *  @param  __first1  Start of first range.
   *  @param  __last1   End of first range.
   *  @param  __first2  Start of second range.
   *  @param  __last2   End of second range.
   *  @param  __comp    The comparison functor.
   *  @return  End of the output range.
   *  @ingroup set_algorithms
   *
   *  This operation iterates over both ranges, copying elements present in
   *  one range but not the other in order to the output range.  Iterators
   *  increment for each range.  When the current element of one range is less
   *  than the other according to @p comp, that element is copied and the
   *  iterator advances.  If an element is contained in both ranges according
   *  to @p __comp, no elements are copied and both ranges advance.  The output
   *  range may not overlap either input range.
  */
  template<typename _InputIterator1, typename _InputIterator2,
	   typename _OutputIterator, typename _Compare>
    _OutputIterator
    set_symmetric_difference(_InputIterator1 __first1, _InputIterator1 __last1,
			     _InputIterator2 __first2, _InputIterator2 __last2,
			     _OutputIterator __result,
			     _Compare __comp)
    {
      typedef typename iterator_traits<_InputIterator1>::value_type
	_ValueType1;
      typedef typename iterator_traits<_InputIterator2>::value_type
	_ValueType2;

      // concept requirements
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
      __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType1>)
      __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
				  _ValueType2>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType1, _ValueType2>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
				  _ValueType2, _ValueType1>)
      __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
      __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);

      while (__first1 != __last1 && __first2 != __last2)
	if (__comp(*__first1, *__first2))
	  {
	    *__result = *__first1;
	    ++__first1;
	    ++__result;
	  }
	else if (__comp(*__first2, *__first1))
	  {
	    *__result = *__first2;
	    ++__first2;
	    ++__result;
	  }
	else
	  {
	    ++__first1;
	    ++__first2;
	  }
      return std::copy(__first2, __last2, 
		       std::copy(__first1, __last1, __result));
    }


  /**
   *  @brief  Return the minimum element in a range.
   *  @ingroup sorting_algorithms
   *  @param  __first  Start of range.
   *  @param  __last   End of range.
   *  @return  Iterator referencing the first instance of the smallest value.
  */
  template<typename _ForwardIterator>
    _ForwardIterator
    min_element(_ForwardIterator __first, _ForwardIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return __first;
      _ForwardIterator __result = __first;
      while (++__first != __last)
	if (*__first < *__result)
	  __result = __first;
      return __result;
    }

  /**
   *  @brief  Return the minimum element in a range using comparison functor.
   *  @ingroup sorting_algorithms
   *  @param  __first  Start of range.
   *  @param  __last   End of range.
   *  @param  __comp   Comparison functor.
   *  @return  Iterator referencing the first instance of the smallest value
   *  according to __comp.
  */
  template<typename _ForwardIterator, typename _Compare>
    _ForwardIterator
    min_element(_ForwardIterator __first, _ForwardIterator __last,
		_Compare __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
	    typename iterator_traits<_ForwardIterator>::value_type,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return __first;
      _ForwardIterator __result = __first;
      while (++__first != __last)
	if (__comp(*__first, *__result))
	  __result = __first;
      return __result;
    }

  /**
   *  @brief  Return the maximum element in a range.
   *  @ingroup sorting_algorithms
   *  @param  __first  Start of range.
   *  @param  __last   End of range.
   *  @return  Iterator referencing the first instance of the largest value.
  */
  template<typename _ForwardIterator>
    _ForwardIterator
    max_element(_ForwardIterator __first, _ForwardIterator __last)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_LessThanComparableConcept<
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last)
	return __first;
      _ForwardIterator __result = __first;
      while (++__first != __last)
	if (*__result < *__first)
	  __result = __first;
      return __result;
    }

  /**
   *  @brief  Return the maximum element in a range using comparison functor.
   *  @ingroup sorting_algorithms
   *  @param  __first  Start of range.
   *  @param  __last   End of range.
   *  @param  __comp   Comparison functor.
   *  @return  Iterator referencing the first instance of the largest value
   *  according to __comp.
  */
  template<typename _ForwardIterator, typename _Compare>
    _ForwardIterator
    max_element(_ForwardIterator __first, _ForwardIterator __last,
		_Compare __comp)
    {
      // concept requirements
      __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
      __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
	    typename iterator_traits<_ForwardIterator>::value_type,
	    typename iterator_traits<_ForwardIterator>::value_type>)
      __glibcxx_requires_valid_range(__first, __last);

      if (__first == __last) return __first;
      _ForwardIterator __result = __first;
      while (++__first != __last)
	if (__comp(*__result, *__first))
	  __result = __first;
      return __result;
    }

_GLIBCXX_END_NAMESPACE_ALGO
} // namespace std

#endif /* _STL_ALGO_H */
