CGAL::collinear

bool	collinear ( Point_2<Kernel> p, Point_2<Kernel> q, Point_2<Kernel> r)
		returns true, iff $$p, $$q, and $$r are collinear.
bool	collinear ( Point_3<Kernel> p, Point_3<Kernel> q, Point_3<Kernel> r)
		returns true, iff $$p, $$q, and $$r are collinear.

See Also