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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 test_elim : forall A B C D Q,
is_midpoint Q B C ->
Py A Q A + Py A Q D = Py Q A Q + Py A Q D.