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(* Formalization of the Chou, Gao and Zhang's decision procedure.          *)
(* Julien Narboux (Julien@narboux.fr)                                      *)
(* LIX/INRIA FUTURS 2004-2006                                              *)
(* University of Strasbourg 2008                                           *)
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(* The line going through the midpoints is parallel to the third side *)

Theorem Conversemenelaus :
forall (A B C D E G : Point) (r1 r2 : F),
mratio D B C r1 ->
mratio E C A r2 ->
inter_ll G D E A B ->
G <> A ->
parallel B G G A ->
B ** G / G ** A = - r1 * r2.