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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_234_1 : forall A B C D O E F,
on_parallel D A B C ->
inter_ll O A C B D ->
on_inter_line_parallel E O B C A B ->
on_inter_line_parallel F O A D A B ->
Col O E F.