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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 l_6_271 : forall B C D G E r,
on_perp_d B C D 1 ->
on_line_d G C D r ->
on_line_d E C B (0-r) ->
perp D E B G.