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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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(* The line going through the midpoints is parallel to the third side *)

Theorem Exo55Hartsshorne :
forall A B C D I J K L,
is_midpoint I A B ->
is_midpoint J B C ->
is_midpoint K C D ->
is_midpoint L D A ->
parallel I J K L /\ parallel I L J K.