bool  fo.operator() ( Kernel::Plane_3 p, Kernel::Point_3 q, Kernel::Point_3 r)  
returns true, iff the signed distance from point q to plane p is smaller than the signed distance from point r to p.  
bool 
 
returns true, iff the signed distance from point q to the plane
p defined by p1, p2, p3 is smaller than the signed distance
from point r to p.
