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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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Lemma l6_197 : forall A B C E F G,
on_foot E A B C ->
on_foot F B A C ->
on_foot G C A B ->
2 * Py A B C * Py B A C * Py A C B * S A B C =
Py A B A * Py B C B * Py A C A * S E F G.