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// -*- C++ -*-

// Copyright (C) 2005, 2006, 2009, 2011 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) 2004 Ami Tavory and Vladimir Dreizin, IBM-HRL.

// Permission to use, copy, modify, sell, and distribute this software

// is hereby granted without fee, provided that the above copyright

// notice appears in all copies, and that both that copyright notice

// and this permission notice appear in supporting documentation. None

// of the above authors, nor IBM Haifa Research Laboratories, make any

// representation about the suitability of this software for any

// purpose. It is provided "as is" without express or implied

// warranty.

/**

 * @file eq_by_less.hpp

 * Contains an equivalence function.

 */

#ifndef PB_DS_EQ_BY_LESS_HPP

#define PB_DS_EQ_BY_LESS_HPP

#include <utility>

#include <functional>

#include <vector>

#include <assert.h>

#include <ext/pb_ds/detail/types_traits.hpp>

namespace __gnu_pbds

{

  namespace detail

  {

    /// Equivalence function.

    template<typename Key, class Cmp_Fn>

    struct eq_by_less : private Cmp_Fn

    {

      bool

      operator()(const Key& r_lhs, const Key& r_rhs) const

      {

        const bool l = Cmp_Fn::operator()(r_lhs, r_rhs);

        const bool g = Cmp_Fn::operator()(r_rhs, r_lhs);

        return !(l || g);

      }

    };

  } // namespace detail

} // namespace __gnu_pbds

#endif // #ifndef PB_DS_EQ_BY_LESS_HPP