(***************************************************************************)
(* Formalization of the Chou, Gao and Zhang's decision procedure.          *)
(* Julien Narboux (Julien@narboux.fr)                                      *)
(* LIX/INRIA FUTURS 2004-2006                                              *)
(* University of Strasbourg 2008                                           *)
(***************************************************************************)
(* on_line *)
(* on_line_d *)
(* inter_ll *)
(* on_parallel_d *)
(* on_perp *)
(* on_perp_d *)
(* on_foot *)

Lemma test_py_on_foot_4  : forall I A B C X,
on_foot I A B C -> Py X I X = Py X I X.