CGAL 5.5  2D and 3D Linear Geometry Kernel

AdaptableFunctor
(with two arguments)CGAL::compare_x()
Operations  
bool  operator() (const Kernel::Point_2 &p, const Kernel::Point_2 &q) 
returns true iff the \( x\)coordinate of p is smaller than the \( x\)coordinate of q .  