(***************************************************************************)
(* Formalization of the Chou, Gao and Zhang's decision procedure.          *)
(* Julien Narboux (Julien@narboux.fr)                                      *)
(* LIX/INRIA FUTURS 2004-2006                                              *)
(* University of Strasbourg 2008-2009                                      *)
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Require Export area_elimination_lemmas.

Theorem on_inter_line_parallel_ex: forall P Q R U V:Point,
~(parallel P Q U V) ->
exists Y:Point, (parallel Y R P Q) /\ (Col Y U V).