(***************************************************************************)
(* 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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Require Export area_method.

Lemma l6_90 : forall A B C E F O,
is_circumcenter O A B C ->
on_foot F C A B ->
on_foot E B A C ->
perp E F A O.