// Set implementation -*- C++ -*-
	
	// Copyright (C) 2001-2019 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) 1996,1997
	 * 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_set.h
	 *  This is an internal header file, included by other library headers.
	 *  Do not attempt to use it directly. @headername{set}
	 */
	
	#ifndef _STL_SET_H
	#define _STL_SET_H 1
	
	#include <bits/concept_check.h>
	#if __cplusplus >= 201103L
	#include <initializer_list>
	#endif
	
	namespace std _GLIBCXX_VISIBILITY(default)
	{
	_GLIBCXX_BEGIN_NAMESPACE_VERSION
	_GLIBCXX_BEGIN_NAMESPACE_CONTAINER
	
	  template<typename _Key, typename _Compare, typename _Alloc>
	    class multiset;
	
	  /**
	   *  @brief A standard container made up of unique keys, which can be
	   *  retrieved in logarithmic time.
	   *
	   *  @ingroup associative_containers
	   *
	   *  @tparam _Key  Type of key objects.
	   *  @tparam _Compare  Comparison function object type, defaults to less<_Key>.
	   *  @tparam _Alloc  Allocator type, defaults to allocator<_Key>.
	   *
	   *  Meets the requirements of a <a href="tables.html#65">container</a>, a
	   *  <a href="tables.html#66">reversible container</a>, and an
	   *  <a href="tables.html#69">associative container</a> (using unique keys).
	   *
	   *  Sets support bidirectional iterators.
	   *
	   *  The private tree data is declared exactly the same way for set and
	   *  multiset; the distinction is made entirely in how the tree functions are
	   *  called (*_unique versus *_equal, same as the standard).
	  */
	  template<typename _Key, typename _Compare = std::less<_Key>,
		   typename _Alloc = std::allocator<_Key> >
	    class set
	    {
	#ifdef _GLIBCXX_CONCEPT_CHECKS
	      // concept requirements
	      typedef typename _Alloc::value_type		_Alloc_value_type;
	# if __cplusplus < 201103L
	      __glibcxx_class_requires(_Key, _SGIAssignableConcept)
	# endif
	      __glibcxx_class_requires4(_Compare, bool, _Key, _Key,
					_BinaryFunctionConcept)
	      __glibcxx_class_requires2(_Key, _Alloc_value_type, _SameTypeConcept)
	#endif
	
	#if __cplusplus >= 201103L
	      static_assert(is_same<typename remove_cv<_Key>::type, _Key>::value,
		  "std::set must have a non-const, non-volatile value_type");
	# ifdef __STRICT_ANSI__
	      static_assert(is_same<typename _Alloc::value_type, _Key>::value,
		  "std::set must have the same value_type as its allocator");
	# endif
	#endif
	
	    public:
	      // typedefs:
	      //@{
	      /// Public typedefs.
	      typedef _Key     key_type;
	      typedef _Key     value_type;
	      typedef _Compare key_compare;
	      typedef _Compare value_compare;
	      typedef _Alloc   allocator_type;
	      //@}
	
	    private:
	      typedef typename __gnu_cxx::__alloc_traits<_Alloc>::template
		rebind<_Key>::other _Key_alloc_type;
	
	      typedef _Rb_tree<key_type, value_type, _Identity<value_type>,
			       key_compare, _Key_alloc_type> _Rep_type;
	      _Rep_type _M_t;  // Red-black tree representing set.
	
	      typedef __gnu_cxx::__alloc_traits<_Key_alloc_type> _Alloc_traits;
	
	    public:
	      //@{
	      ///  Iterator-related typedefs.
	      typedef typename _Alloc_traits::pointer		 pointer;
	      typedef typename _Alloc_traits::const_pointer	 const_pointer;
	      typedef typename _Alloc_traits::reference		 reference;
	      typedef typename _Alloc_traits::const_reference	 const_reference;
	      // _GLIBCXX_RESOLVE_LIB_DEFECTS
	      // DR 103. set::iterator is required to be modifiable,
	      // but this allows modification of keys.
	      typedef typename _Rep_type::const_iterator	 iterator;
	      typedef typename _Rep_type::const_iterator	 const_iterator;
	      typedef typename _Rep_type::const_reverse_iterator reverse_iterator;
	      typedef typename _Rep_type::const_reverse_iterator const_reverse_iterator;
	      typedef typename _Rep_type::size_type		 size_type;
	      typedef typename _Rep_type::difference_type	 difference_type;
	      //@}
	
	#if __cplusplus > 201402L
	      using node_type = typename _Rep_type::node_type;
	      using insert_return_type = typename _Rep_type::insert_return_type;
	#endif
	
	      // allocation/deallocation
	      /**
	       *  @brief  Default constructor creates no elements.
	       */
	#if __cplusplus < 201103L
	      set() : _M_t() { }
	#else
	      set() = default;
	#endif
	
	      /**
	       *  @brief  Creates a %set with no elements.
	       *  @param  __comp  Comparator to use.
	       *  @param  __a  An allocator object.
	       */
	      explicit
	      set(const _Compare& __comp,
		  const allocator_type& __a = allocator_type())
	      : _M_t(__comp, _Key_alloc_type(__a)) { }
	
	      /**
	       *  @brief  Builds a %set from a range.
	       *  @param  __first  An input iterator.
	       *  @param  __last  An input iterator.
	       *
	       *  Create a %set consisting of copies of the elements from
	       *  [__first,__last).  This is linear in N if the range is
	       *  already sorted, and NlogN otherwise (where N is
	       *  distance(__first,__last)).
	       */
	      template<typename _InputIterator>
		set(_InputIterator __first, _InputIterator __last)
		: _M_t()
		{ _M_t._M_insert_range_unique(__first, __last); }
	
	      /**
	       *  @brief  Builds a %set from a range.
	       *  @param  __first  An input iterator.
	       *  @param  __last  An input iterator.
	       *  @param  __comp  A comparison functor.
	       *  @param  __a  An allocator object.
	       *
	       *  Create a %set consisting of copies of the elements from
	       *  [__first,__last).  This is linear in N if the range is
	       *  already sorted, and NlogN otherwise (where N is
	       *  distance(__first,__last)).
	       */
	      template<typename _InputIterator>
		set(_InputIterator __first, _InputIterator __last,
		    const _Compare& __comp,
		    const allocator_type& __a = allocator_type())
		: _M_t(__comp, _Key_alloc_type(__a))
		{ _M_t._M_insert_range_unique(__first, __last); }
	
	      /**
	       *  @brief  %Set copy constructor.
	       *
	       *  Whether the allocator is copied depends on the allocator traits.
	       */
	#if __cplusplus < 201103L
	      set(const set& __x)
	      : _M_t(__x._M_t) { }
	#else
	      set(const set&) = default;
	
	     /**
	       *  @brief %Set move constructor
	       *
	       *  The newly-created %set contains the exact contents of the moved
	       *  instance. The moved instance is a valid, but unspecified, %set.
	       */
	      set(set&&) = default;
	
	      /**
	       *  @brief  Builds a %set from an initializer_list.
	       *  @param  __l  An initializer_list.
	       *  @param  __comp  A comparison functor.
	       *  @param  __a  An allocator object.
	       *
	       *  Create a %set consisting of copies of the elements in the list.
	       *  This is linear in N if the list is already sorted, and NlogN
	       *  otherwise (where N is @a __l.size()).
	       */
	      set(initializer_list<value_type> __l,
		  const _Compare& __comp = _Compare(),
		  const allocator_type& __a = allocator_type())
	      : _M_t(__comp, _Key_alloc_type(__a))
	      { _M_t._M_insert_range_unique(__l.begin(), __l.end()); }
	
	      /// Allocator-extended default constructor.
	      explicit
	      set(const allocator_type& __a)
	      : _M_t(_Key_alloc_type(__a)) { }
	
	      /// Allocator-extended copy constructor.
	      set(const set& __x, const allocator_type& __a)
	      : _M_t(__x._M_t, _Key_alloc_type(__a)) { }
	
	      /// Allocator-extended move constructor.
	      set(set&& __x, const allocator_type& __a)
	      noexcept(is_nothrow_copy_constructible<_Compare>::value
		       && _Alloc_traits::_S_always_equal())
	      : _M_t(std::move(__x._M_t), _Key_alloc_type(__a)) { }
	
	      /// Allocator-extended initialier-list constructor.
	      set(initializer_list<value_type> __l, const allocator_type& __a)
	      : _M_t(_Key_alloc_type(__a))
	      { _M_t._M_insert_range_unique(__l.begin(), __l.end()); }
	
	      /// Allocator-extended range constructor.
	      template<typename _InputIterator>
		set(_InputIterator __first, _InputIterator __last,
		    const allocator_type& __a)
		: _M_t(_Key_alloc_type(__a))
		{ _M_t._M_insert_range_unique(__first, __last); }
	
	      /**
	       *  The dtor only erases the elements, and note that if the elements
	       *  themselves are pointers, the pointed-to memory is not touched in any
	       *  way. Managing the pointer is the user's responsibility.
	       */
	      ~set() = default;
	#endif
	
	      /**
	       *  @brief  %Set assignment operator.
	       *
	       *  Whether the allocator is copied depends on the allocator traits.
	       */
	#if __cplusplus < 201103L
	      set&
	      operator=(const set& __x)
	      {
		_M_t = __x._M_t;
		return *this;
	      }
	#else
	      set&
	      operator=(const set&) = default;
	
	      /// Move assignment operator.
	      set&

	      operator=(set&&) = default;
	
	      /**
	       *  @brief  %Set list assignment operator.
	       *  @param  __l  An initializer_list.
	       *
	       *  This function fills a %set with copies of the elements in the
	       *  initializer list @a __l.
	       *
	       *  Note that the assignment completely changes the %set and
	       *  that the resulting %set's size is the same as the number
	       *  of elements assigned.
	       */
	      set&
	      operator=(initializer_list<value_type> __l)
	      {
		_M_t._M_assign_unique(__l.begin(), __l.end());
		return *this;
	      }
	#endif
	
	      // accessors:
	
	      ///  Returns the comparison object with which the %set was constructed.
	      key_compare
	      key_comp() const
	      { return _M_t.key_comp(); }
	      ///  Returns the comparison object with which the %set was constructed.
	      value_compare
	      value_comp() const
	      { return _M_t.key_comp(); }
	      ///  Returns the allocator object with which the %set was constructed.
	      allocator_type
	      get_allocator() const _GLIBCXX_NOEXCEPT
	      { return allocator_type(_M_t.get_allocator()); }
	
	      /**
	       *  Returns a read-only (constant) iterator that points to the first
	       *  element in the %set.  Iteration is done in ascending order according
	       *  to the keys.
	       */
	      iterator
	      begin() const _GLIBCXX_NOEXCEPT
	      { return _M_t.begin(); }
	
	      /**
	       *  Returns a read-only (constant) iterator that points one past the last
	       *  element in the %set.  Iteration is done in ascending order according
	       *  to the keys.
	       */
	      iterator
	      end() const _GLIBCXX_NOEXCEPT
	      { return _M_t.end(); }
	
	      /**
	       *  Returns a read-only (constant) iterator that points to the last
	       *  element in the %set.  Iteration is done in descending order according
	       *  to the keys.
	       */
	      reverse_iterator
	      rbegin() const _GLIBCXX_NOEXCEPT
	      { return _M_t.rbegin(); }
	
	      /**
	       *  Returns a read-only (constant) reverse iterator that points to the
	       *  last pair in the %set.  Iteration is done in descending order
	       *  according to the keys.
	       */
	      reverse_iterator
	      rend() const _GLIBCXX_NOEXCEPT
	      { return _M_t.rend(); }
	
	#if __cplusplus >= 201103L
	      /**
	       *  Returns a read-only (constant) iterator that points to the first
	       *  element in the %set.  Iteration is done in ascending order according
	       *  to the keys.
	       */
	      iterator
	      cbegin() const noexcept
	      { return _M_t.begin(); }
	
	      /**
	       *  Returns a read-only (constant) iterator that points one past the last
	       *  element in the %set.  Iteration is done in ascending order according
	       *  to the keys.
	       */
	      iterator
	      cend() const noexcept
	      { return _M_t.end(); }
	
	      /**
	       *  Returns a read-only (constant) iterator that points to the last
	       *  element in the %set.  Iteration is done in descending order according
	       *  to the keys.
	       */
	      reverse_iterator
	      crbegin() const noexcept
	      { return _M_t.rbegin(); }
	
	      /**
	       *  Returns a read-only (constant) reverse iterator that points to the
	       *  last pair in the %set.  Iteration is done in descending order
	       *  according to the keys.
	       */
	      reverse_iterator
	      crend() const noexcept
	      { return _M_t.rend(); }
	#endif
	
	      ///  Returns true if the %set is empty.
	      _GLIBCXX_NODISCARD bool
	      empty() const _GLIBCXX_NOEXCEPT
	      { return _M_t.empty(); }
	
	      ///  Returns the size of the %set.
	      size_type
	      size() const _GLIBCXX_NOEXCEPT
	      { return _M_t.size(); }
	
	      ///  Returns the maximum size of the %set.
	      size_type
	      max_size() const _GLIBCXX_NOEXCEPT
	      { return _M_t.max_size(); }
	
	      /**
	       *  @brief  Swaps data with another %set.
	       *  @param  __x  A %set of the same element and allocator types.
	       *
	       *  This exchanges the elements between two sets in constant
	       *  time.  (It is only swapping a pointer, an integer, and an
	       *  instance of the @c Compare type (which itself is often
	       *  stateless and empty), so it should be quite fast.)  Note
	       *  that the global std::swap() function is specialized such
	       *  that std::swap(s1,s2) will feed to this function.
	       *
	       *  Whether the allocators are swapped depends on the allocator traits.
	       */
	      void
	      swap(set& __x)
	      _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Compare>::value)
	      { _M_t.swap(__x._M_t); }
	
	      // insert/erase
	#if __cplusplus >= 201103L
	      /**
	       *  @brief Attempts to build and insert an element into the %set.
	       *  @param __args  Arguments used to generate an element.
	       *  @return  A pair, of which the first element is an iterator that points
	       *           to the possibly inserted element, and the second is a bool
	       *           that is true if the element was actually inserted.
	       *
	       *  This function attempts to build and insert an element into the %set.
	       *  A %set relies on unique keys and thus an element is only inserted if
	       *  it is not already present in the %set.
	       *
	       *  Insertion requires logarithmic time.
	       */
	      template<typename... _Args>
		std::pair<iterator, bool>
		emplace(_Args&&... __args)
		{ return _M_t._M_emplace_unique(std::forward<_Args>(__args)...); }
	
	      /**
	       *  @brief Attempts to insert an element into the %set.
	       *  @param  __pos  An iterator that serves as a hint as to where the
	       *                element should be inserted.
	       *  @param  __args  Arguments used to generate the element to be
	       *                 inserted.
	       *  @return An iterator that points to the element with key equivalent to
	       *          the one generated from @a __args (may or may not be the
	       *          element itself).
	       *
	       *  This function is not concerned about whether the insertion took place,
	       *  and thus does not return a boolean like the single-argument emplace()
	       *  does.  Note that the first parameter is only a hint and can
	       *  potentially improve the performance of the insertion process.  A bad
	       *  hint would cause no gains in efficiency.
	       *
	       *  For more on @a hinting, see:
	       *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints
	       *
	       *  Insertion requires logarithmic time (if the hint is not taken).
	       */
	      template<typename... _Args>
		iterator
		emplace_hint(const_iterator __pos, _Args&&... __args)
		{
		  return _M_t._M_emplace_hint_unique(__pos,
						     std::forward<_Args>(__args)...);
		}
	#endif
	
	      /**
	       *  @brief Attempts to insert an element into the %set.
	       *  @param  __x  Element to be inserted.
	       *  @return  A pair, of which the first element is an iterator that points
	       *           to the possibly inserted element, and the second is a bool
	       *           that is true if the element was actually inserted.
	       *
	       *  This function attempts to insert an element into the %set.  A %set
	       *  relies on unique keys and thus an element is only inserted if it is
	       *  not already present in the %set.
	       *
	       *  Insertion requires logarithmic time.
	       */
	      std::pair<iterator, bool>
	      insert(const value_type& __x)
	      {
		std::pair<typename _Rep_type::iterator, bool> __p =
		  _M_t._M_insert_unique(__x);
		return std::pair<iterator, bool>(__p.first, __p.second);
	      }
	
	#if __cplusplus >= 201103L
	      std::pair<iterator, bool>
	      insert(value_type&& __x)
	      {
		std::pair<typename _Rep_type::iterator, bool> __p =
		  _M_t._M_insert_unique(std::move(__x));
		return std::pair<iterator, bool>(__p.first, __p.second);
	      }
	#endif
	
	      /**
	       *  @brief Attempts to insert an element into the %set.
	       *  @param  __position  An iterator that serves as a hint as to where the
	       *                    element should be inserted.
	       *  @param  __x  Element to be inserted.
	       *  @return An iterator that points to the element with key of
	       *           @a __x (may or may not be the element passed in).
	       *
	       *  This function is not concerned about whether the insertion took place,
	       *  and thus does not return a boolean like the single-argument insert()
	       *  does.  Note that the first parameter is only a hint and can
	       *  potentially improve the performance of the insertion process.  A bad
	       *  hint would cause no gains in efficiency.
	       *
	       *  For more on @a hinting, see:
	       *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints
	       *
	       *  Insertion requires logarithmic time (if the hint is not taken).
	       */
	      iterator
	      insert(const_iterator __position, const value_type& __x)
	      { return _M_t._M_insert_unique_(__position, __x); }
	
	#if __cplusplus >= 201103L
	      iterator
	      insert(const_iterator __position, value_type&& __x)
	      { return _M_t._M_insert_unique_(__position, std::move(__x)); }
	#endif
	
	      /**
	       *  @brief A template function that attempts to insert a range
	       *  of elements.
	       *  @param  __first  Iterator pointing to the start of the range to be
	       *                   inserted.
	       *  @param  __last  Iterator pointing to the end of the range.
	       *
	       *  Complexity similar to that of the range constructor.
	       */
	      template<typename _InputIterator>
		void
		insert(_InputIterator __first, _InputIterator __last)
		{ _M_t._M_insert_range_unique(__first, __last); }
	
	#if __cplusplus >= 201103L
	      /**
	       *  @brief Attempts to insert a list of elements into the %set.
	       *  @param  __l  A std::initializer_list<value_type> of elements
	       *               to be inserted.
	       *
	       *  Complexity similar to that of the range constructor.
	       */
	      void
	      insert(initializer_list<value_type> __l)
	      { this->insert(__l.begin(), __l.end()); }
	#endif
	
	#if __cplusplus > 201402L
	      /// Extract a node.
	      node_type
	      extract(const_iterator __pos)
	      {
		__glibcxx_assert(__pos != end());
		return _M_t.extract(__pos);
	      }
	
	      /// Extract a node.
	      node_type
	      extract(const key_type& __x)
	      { return _M_t.extract(__x); }
	
	      /// Re-insert an extracted node.
	      insert_return_type
	      insert(node_type&& __nh)
	      { return _M_t._M_reinsert_node_unique(std::move(__nh)); }
	
	      /// Re-insert an extracted node.
	      iterator
	      insert(const_iterator __hint, node_type&& __nh)
	      { return _M_t._M_reinsert_node_hint_unique(__hint, std::move(__nh)); }
	
	      template<typename, typename>
		friend class std::_Rb_tree_merge_helper;
	
	      template<typename _Compare1>
		void
		merge(set<_Key, _Compare1, _Alloc>& __source)
		{
		  using _Merge_helper = _Rb_tree_merge_helper<set, _Compare1>;
		  _M_t._M_merge_unique(_Merge_helper::_S_get_tree(__source));
		}
	
	      template<typename _Compare1>
		void
		merge(set<_Key, _Compare1, _Alloc>&& __source)
		{ merge(__source); }
	
	      template<typename _Compare1>
		void
		merge(multiset<_Key, _Compare1, _Alloc>& __source)
		{
		  using _Merge_helper = _Rb_tree_merge_helper<set, _Compare1>;
		  _M_t._M_merge_unique(_Merge_helper::_S_get_tree(__source));
		}
	
	      template<typename _Compare1>
		void
		merge(multiset<_Key, _Compare1, _Alloc>&& __source)
		{ merge(__source); }
	#endif // C++17
	
	#if __cplusplus >= 201103L
	      // _GLIBCXX_RESOLVE_LIB_DEFECTS
	      // DR 130. Associative erase should return an iterator.
	      /**
	       *  @brief Erases an element from a %set.
	       *  @param  __position  An iterator pointing to the element to be erased.
	       *  @return An iterator pointing to the element immediately following
	       *          @a __position prior to the element being erased. If no such
	       *          element exists, end() is returned.
	       *
	       *  This function erases an element, pointed to by the given iterator,
	       *  from a %set.  Note that this function only erases the element, and
	       *  that if the element is itself a pointer, the pointed-to memory is not
	       *  touched in any way.  Managing the pointer is the user's
	       *  responsibility.
	       */
	      _GLIBCXX_ABI_TAG_CXX11
	      iterator
	      erase(const_iterator __position)
	      { return _M_t.erase(__position); }
	#else
	      /**
	       *  @brief Erases an element from a %set.
	       *  @param  position  An iterator pointing to the element to be erased.
	       *
	       *  This function erases an element, pointed to by the given iterator,
	       *  from a %set.  Note that this function only erases the element, and
	       *  that if the element is itself a pointer, the pointed-to memory is not
	       *  touched in any way.  Managing the pointer is the user's
	       *  responsibility.
	       */
	      void
	      erase(iterator __position)
	      { _M_t.erase(__position); }
	#endif
	
	      /**
	       *  @brief Erases elements according to the provided key.
	       *  @param  __x  Key of element to be erased.
	       *  @return  The number of elements erased.
	       *
	       *  This function erases all the elements located by the given key from
	       *  a %set.
	       *  Note that this function only erases the element, and that if
	       *  the element is itself a pointer, the pointed-to memory is not touched
	       *  in any way.  Managing the pointer is the user's responsibility.
	       */
	      size_type
	      erase(const key_type& __x)
	      { return _M_t.erase(__x); }
	
	#if __cplusplus >= 201103L
	      // _GLIBCXX_RESOLVE_LIB_DEFECTS
	      // DR 130. Associative erase should return an iterator.
	      /**
	       *  @brief Erases a [__first,__last) range of elements from a %set.
	       *  @param  __first  Iterator pointing to the start of the range to be
	       *                 erased.
	
	       *  @param __last Iterator pointing to the end of the range to
	       *  be erased.
	       *  @return The iterator @a __last.
	       *
	       *  This function erases a sequence of elements from a %set.
	       *  Note that this function only erases the element, and that if
	       *  the element is itself a pointer, the pointed-to memory is not touched
	       *  in any way.  Managing the pointer is the user's responsibility.
	       */
	      _GLIBCXX_ABI_TAG_CXX11
	      iterator
	      erase(const_iterator __first, const_iterator __last)
	      { return _M_t.erase(__first, __last); }
	#else
	      /**
	       *  @brief Erases a [first,last) range of elements from a %set.
	       *  @param  __first  Iterator pointing to the start of the range to be
	       *                 erased.
	       *  @param __last Iterator pointing to the end of the range to
	       *  be erased.
	       *
	       *  This function erases a sequence of elements from a %set.
	       *  Note that this function only erases the element, and that if
	       *  the element is itself a pointer, the pointed-to memory is not touched
	       *  in any way.  Managing the pointer is the user's responsibility.
	       */
	      void
	      erase(iterator __first, iterator __last)
	      { _M_t.erase(__first, __last); }
	#endif
	
	      /**
	       *  Erases all elements in a %set.  Note that this function only erases
	       *  the elements, and that if the elements themselves are pointers, the
	       *  pointed-to memory is not touched in any way.  Managing the pointer is
	       *  the user's responsibility.
	       */
	      void
	      clear() _GLIBCXX_NOEXCEPT
	      { _M_t.clear(); }
	
	      // set operations:
	
	      //@{
	      /**
	       *  @brief  Finds the number of elements.
	       *  @param  __x  Element to located.
	       *  @return  Number of elements with specified key.
	       *
	       *  This function only makes sense for multisets; for set the result will
	       *  either be 0 (not present) or 1 (present).
	       */
	      size_type
	      count(const key_type& __x) const
	      { return _M_t.find(__x) == _M_t.end() ? 0 : 1; }
	
	#if __cplusplus > 201103L
	      template<typename _Kt>
		auto
		count(const _Kt& __x) const
		-> decltype(_M_t._M_count_tr(__x))
		{ return _M_t._M_count_tr(__x); }
	#endif
	      //@}
	
	#if __cplusplus > 201703L
	      //@{
	      /**
	       *  @brief  Finds whether an element with the given key exists.
	       *  @param  __x  Key of elements to be located.
	       *  @return  True if there is an element with the specified key.
	       */
	      bool
	      contains(const key_type& __x) const
	      { return _M_t.find(__x) != _M_t.end(); }
	
	      template<typename _Kt>
		auto
		contains(const _Kt& __x) const
		-> decltype(_M_t._M_find_tr(__x), void(), true)
		{ return _M_t._M_find_tr(__x) != _M_t.end(); }
	      //@}
	#endif
	
	      // _GLIBCXX_RESOLVE_LIB_DEFECTS
	      // 214.  set::find() missing const overload
	      //@{
	      /**
	       *  @brief Tries to locate an element in a %set.
	       *  @param  __x  Element to be located.
	       *  @return  Iterator pointing to sought-after element, or end() if not
	       *           found.
	       *
	       *  This function takes a key and tries to locate the element with which
	       *  the key matches.  If successful the function returns an iterator
	       *  pointing to the sought after element.  If unsuccessful it returns the
	       *  past-the-end ( @c end() ) iterator.
	       */
	      iterator
	      find(const key_type& __x)
	      { return _M_t.find(__x); }
	
	      const_iterator
	      find(const key_type& __x) const
	      { return _M_t.find(__x); }
	
	#if __cplusplus > 201103L
	      template<typename _Kt>
		auto
		find(const _Kt& __x)
		-> decltype(iterator{_M_t._M_find_tr(__x)})
		{ return iterator{_M_t._M_find_tr(__x)}; }
	
	      template<typename _Kt>
		auto
		find(const _Kt& __x) const
		-> decltype(const_iterator{_M_t._M_find_tr(__x)})
		{ return const_iterator{_M_t._M_find_tr(__x)}; }
	#endif
	      //@}
	
	      //@{
	      /**
	       *  @brief Finds the beginning of a subsequence matching given key.
	       *  @param  __x  Key to be located.
	       *  @return  Iterator pointing to first element equal to or greater
	       *           than key, or end().
	       *
	       *  This function returns the first element of a subsequence of elements
	       *  that matches the given key.  If unsuccessful it returns an iterator
	       *  pointing to the first element that has a greater value than given key
	       *  or end() if no such element exists.
	       */
	      iterator
	      lower_bound(const key_type& __x)
	      { return _M_t.lower_bound(__x); }
	
	      const_iterator
	      lower_bound(const key_type& __x) const
	      { return _M_t.lower_bound(__x); }
	
	#if __cplusplus > 201103L
	      template<typename _Kt>
		auto
		lower_bound(const _Kt& __x)
		-> decltype(iterator(_M_t._M_lower_bound_tr(__x)))
		{ return iterator(_M_t._M_lower_bound_tr(__x)); }
	
	      template<typename _Kt>
		auto
		lower_bound(const _Kt& __x) const
		-> decltype(const_iterator(_M_t._M_lower_bound_tr(__x)))
		{ return const_iterator(_M_t._M_lower_bound_tr(__x)); }
	#endif
	      //@}
	
	      //@{
	      /**
	       *  @brief Finds the end of a subsequence matching given key.
	       *  @param  __x  Key to be located.
	       *  @return Iterator pointing to the first element
	       *          greater than key, or end().
	       */
	      iterator
	      upper_bound(const key_type& __x)
	      { return _M_t.upper_bound(__x); }
	
	      const_iterator
	      upper_bound(const key_type& __x) const
	      { return _M_t.upper_bound(__x); }
	
	#if __cplusplus > 201103L
	      template<typename _Kt>
		auto
		upper_bound(const _Kt& __x)
		-> decltype(iterator(_M_t._M_upper_bound_tr(__x)))
		{ return iterator(_M_t._M_upper_bound_tr(__x)); }
	
	      template<typename _Kt>
		auto
		upper_bound(const _Kt& __x) const
		-> decltype(iterator(_M_t._M_upper_bound_tr(__x)))
		{ return const_iterator(_M_t._M_upper_bound_tr(__x)); }
	#endif
	      //@}
	
	      //@{
	      /**
	       *  @brief Finds a subsequence matching given key.
	       *  @param  __x  Key to be located.
	       *  @return  Pair of iterators that possibly points to the subsequence
	       *           matching given key.
	       *
	       *  This function is equivalent to
	       *  @code
	       *    std::make_pair(c.lower_bound(val),
	       *                   c.upper_bound(val))
	       *  @endcode
	       *  (but is faster than making the calls separately).
	       *
	       *  This function probably only makes sense for multisets.
	       */
	      std::pair<iterator, iterator>
	      equal_range(const key_type& __x)
	      { return _M_t.equal_range(__x); }
	
	      std::pair<const_iterator, const_iterator>
	      equal_range(const key_type& __x) const
	      { return _M_t.equal_range(__x); }
	
	#if __cplusplus > 201103L
	      template<typename _Kt>
		auto
		equal_range(const _Kt& __x)
		-> decltype(pair<iterator, iterator>(_M_t._M_equal_range_tr(__x)))
		{ return pair<iterator, iterator>(_M_t._M_equal_range_tr(__x)); }
	
	      template<typename _Kt>
		auto
		equal_range(const _Kt& __x) const
		-> decltype(pair<iterator, iterator>(_M_t._M_equal_range_tr(__x)))
		{ return pair<iterator, iterator>(_M_t._M_equal_range_tr(__x)); }
	#endif
	      //@}
	
	      template<typename _K1, typename _C1, typename _A1>
		friend bool
		operator==(const set<_K1, _C1, _A1>&, const set<_K1, _C1, _A1>&);
	
	      template<typename _K1, typename _C1, typename _A1>
		friend bool
		operator<(const set<_K1, _C1, _A1>&, const set<_K1, _C1, _A1>&);
	    };
	
	#if __cpp_deduction_guides >= 201606
	
	  template<typename _InputIterator,
		   typename _Compare =
		     less<typename iterator_traits<_InputIterator>::value_type>,
		   typename _Allocator =
		     allocator<typename iterator_traits<_InputIterator>::value_type>,
		   typename = _RequireInputIter<_InputIterator>,
		   typename = _RequireNotAllocator<_Compare>,
		   typename = _RequireAllocator<_Allocator>>
	    set(_InputIterator, _InputIterator,
		_Compare = _Compare(), _Allocator = _Allocator())
	    -> set<typename iterator_traits<_InputIterator>::value_type,
		  _Compare, _Allocator>;
	
	  template<typename _Key, typename _Compare = less<_Key>,
		   typename _Allocator = allocator<_Key>,
		   typename = _RequireNotAllocator<_Compare>,
		   typename = _RequireAllocator<_Allocator>>
	    set(initializer_list<_Key>,
		_Compare = _Compare(), _Allocator = _Allocator())
	    -> set<_Key, _Compare, _Allocator>;
	
	  template<typename _InputIterator, typename _Allocator,
		   typename = _RequireInputIter<_InputIterator>,
		   typename = _RequireAllocator<_Allocator>>
	    set(_InputIterator, _InputIterator, _Allocator)
	    -> set<typename iterator_traits<_InputIterator>::value_type,
		   less<typename iterator_traits<_InputIterator>::value_type>,
		   _Allocator>;
	
	  template<typename _Key, typename _Allocator,
		   typename = _RequireAllocator<_Allocator>>
	    set(initializer_list<_Key>, _Allocator)
	    -> set<_Key, less<_Key>, _Allocator>;
	
	#endif
	
	  /**
	   *  @brief  Set equality comparison.
	   *  @param  __x  A %set.
	   *  @param  __y  A %set of the same type as @a x.
	   *  @return  True iff the size and elements of the sets are equal.
	   *
	   *  This is an equivalence relation.  It is linear in the size of the sets.
	   *  Sets are considered equivalent if their sizes are equal, and if
	   *  corresponding elements compare equal.
	  */
	  template<typename _Key, typename _Compare, typename _Alloc>
	    inline bool
	    operator==(const set<_Key, _Compare, _Alloc>& __x,
		       const set<_Key, _Compare, _Alloc>& __y)
	    { return __x._M_t == __y._M_t; }
	
	  /**
	   *  @brief  Set ordering relation.
	   *  @param  __x  A %set.
	   *  @param  __y  A %set of the same type as @a x.
	   *  @return  True iff @a __x is lexicographically less than @a __y.
	   *
	   *  This is a total ordering relation.  It is linear in the size of the
	   *  sets.  The elements must be comparable with @c <.
	   *
	   *  See std::lexicographical_compare() for how the determination is made.
	  */
	  template<typename _Key, typename _Compare, typename _Alloc>
	    inline bool
	    operator<(const set<_Key, _Compare, _Alloc>& __x,
		      const set<_Key, _Compare, _Alloc>& __y)
	    { return __x._M_t < __y._M_t; }
	
	  ///  Returns !(x == y).
	  template<typename _Key, typename _Compare, typename _Alloc>
	    inline bool
	    operator!=(const set<_Key, _Compare, _Alloc>& __x,
		       const set<_Key, _Compare, _Alloc>& __y)
	    { return !(__x == __y); }
	
	  ///  Returns y < x.
	  template<typename _Key, typename _Compare, typename _Alloc>
	    inline bool
	    operator>(const set<_Key, _Compare, _Alloc>& __x,
		      const set<_Key, _Compare, _Alloc>& __y)
	    { return __y < __x; }
	
	  ///  Returns !(y < x)
	  template<typename _Key, typename _Compare, typename _Alloc>
	    inline bool
	    operator<=(const set<_Key, _Compare, _Alloc>& __x,
		       const set<_Key, _Compare, _Alloc>& __y)
	    { return !(__y < __x); }
	
	  ///  Returns !(x < y)
	  template<typename _Key, typename _Compare, typename _Alloc>
	    inline bool
	    operator>=(const set<_Key, _Compare, _Alloc>& __x,
		       const set<_Key, _Compare, _Alloc>& __y)
	    { return !(__x < __y); }
	
	  /// See std::set::swap().
	  template<typename _Key, typename _Compare, typename _Alloc>
	    inline void
	    swap(set<_Key, _Compare, _Alloc>& __x, set<_Key, _Compare, _Alloc>& __y)
	    _GLIBCXX_NOEXCEPT_IF(noexcept(__x.swap(__y)))
	    { __x.swap(__y); }
	
	_GLIBCXX_END_NAMESPACE_CONTAINER
	
	#if __cplusplus > 201402L
	  // Allow std::set access to internals of compatible sets.
	  template<typename _Val, typename _Cmp1, typename _Alloc, typename _Cmp2>
	    struct
	    _Rb_tree_merge_helper<_GLIBCXX_STD_C::set<_Val, _Cmp1, _Alloc>, _Cmp2>
	    {
	    private:
	      friend class _GLIBCXX_STD_C::set<_Val, _Cmp1, _Alloc>;
	
	      static auto&
	      _S_get_tree(_GLIBCXX_STD_C::set<_Val, _Cmp2, _Alloc>& __set)
	      { return __set._M_t; }
	
	      static auto&
	      _S_get_tree(_GLIBCXX_STD_C::multiset<_Val, _Cmp2, _Alloc>& __set)
	      { return __set._M_t; }
	    };
	#endif // C++17
	
	_GLIBCXX_END_NAMESPACE_VERSION
	} //namespace std
	#endif /* _STL_SET_H */