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

Theorem th2_41 :
forall A B C D P Q M : Point,
on_line C A P ->
on_inter_line_parallel D C B P A B ->
inter_ll Q A D B C ->
inter_ll M A B P Q ->
B <> M ->
parallel A M B M ->
C<>D ->
A ** M / B ** M = - (1).