
A model of this concept must provide:

Comparison_result  operator() (const Kernel::Line_2 &l1, const Kernel::Line_2 &l2) 
 compares the slopes of the lines l1 and l2


Comparison_result  operator() (const Kernel::Segment_2 &s1, const Kernel::Segment_2 &s2) 
 compares the slopes of the segments s1 and s2 , where the slope is the variation of the y coordinate from the left to the right endpoint of the segments.


Comparison_result  operator() (const Kernel::Point_2 &s1s, const Kernel::Point_2 &s1t, const Kernel::Point_2 &s2s, const Kernel::Point_2 &s2t)) 
 compares the slopes of the segments (s1s,s1t) and (s2s,s2t) , where the slope is the variation of the y coordinate from the left to the right endpoint of the segments.

