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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 th6_232 : forall A B C D P Q,
on_parallel_d D A B C 1 ->
is_midpoint P B D ->
is_midpoint Q A C ->
parallel P Q A B.