CGAL 5.6  2D and 3D Linear Geometry Kernel

AdaptableBinaryFunction
CGAL::compare_xy()
Operations  
Comparison_result  operator() (const Kernel::Point_3 &p, const Kernel::Point_3 &q) 
Compares the Cartesian coordinates of points p and q lexicographically in \( xy\) order: first \( x\)coordinates are compared, if they are equal, \( y\)coordinates are compared.  