CGAL 6.0.1  2D and 3D Linear Geometry Kernel

AdaptableQuaternaryFunction
Operations  
A model of this concept must provide:  
Comparison_result  operator() (const Kernel::Point_2 &p, const Kernel::Point_2 &q, const Kernel::Point_2 &r, const Kernel::Point_2 &s) 
compares the signed distance of r and s to the directed line through p and q .  
Comparison_result  operator() (const Kernel::Line_2 &l, const Kernel::Point_2 &r, const Kernel::Point_2 &s) 
compares the signed distance of r and s to the directed line l .  