abstract class IntersectionFinder {
 bool segment_segment(Vector3 a1, Vector3 a2, Vector3 b1, Vector3 b2, Vector4 acol);
 bool segment_sphere(Vector3 s1, Vector3 s2, Vector3 c, double r);
 bool sphere_sphere(Vector3 ca, double ra, Vector3 cb, double rb);
 bool aabb_aabb(Aabb3 b1, Aabb3 b2 );
 bool poly_poly(List<Vector3> a, List<Vector3> b);
}