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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_52 : forall A B C D E F,
is_midpoint E A C ->
is_midpoint F A B ->
is_midpoint D B C ->
2*(Py A D A)+2*(Py F C F) +2*Py B E B =
(2+1)/2 * (Py A C A + Py A B A + Py B C B).