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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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(** nine point circle *)
(** another statement for nine point circle theorem *)

Lemma nine_point_1 : forall A B C A' B' C' M,
is_midpoint A' B C ->
is_midpoint B' A C ->
is_midpoint C' A B ->
on_foot M A B C ->
co_circle M A' B' C'.