// Copyright (c) 2000  Max-Planck-Institute Saarbruecken (Germany).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org).
// 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 of the License, or (at your option) any later version.
//
// Licensees holding a valid commercial license may use this file in
// accordance with the commercial license agreement provided with the software.
//
// This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
// WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
//
// $URL$
// $Id$
// 
//
// Author(s)     : Susan Hert <hert@mpi-sb.mpg.de>

#ifndef CGAL_POINT_PAIR_LESS_XY_2_H
#define CGAL_POINT_PAIR_LESS_XY_2_H

#include <utility>

namespace CGAL {

//
// Given two pairs of points determine their lexicographical order by first
// comparing the first points lexicographically and then the second points if
// the first are equal
//
template <class Traits>
class Point_pair_less_xy_2
{
   typedef typename Traits::Point_2           Point_2;
   typedef std::pair<Point_2, Point_2>        Point_pair;
   typedef typename Traits::Less_xy_2         Less_xy_2;

   public:
     Point_pair_less_xy_2() : _less_xy_2(Traits().less_xy_2_object())
     { }
     

     bool 
     operator()(const Point_pair& p, const Point_pair& q) const
     { 
        if (_less_xy_2(p.first, q.first))
            return true;
        else if (_less_xy_2(q.first, p.first))
            return false;
        else if (_less_xy_2(p.second, q.second))
            return true;
        else
            return false;
     }

   private:
      Less_xy_2 _less_xy_2;
};

}

#endif // CGAL_POINT_PAIR_LESS_XY_H
