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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_55 : forall A B C E G,
is_midpoint E A C ->
on_line_d G B E (2/(2+1)) ->
1+2 <> 0 ->
(2+1) * (Py A G A + Py G C G + Py B G B) =
Py A C A + Py A B A + Py B C B.