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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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(** Transitivity of the parallel predicate expressed constructively *)

(* Specifications: *)
Theorem parallel_transitivity :
forall A B C D E F : Point,
A <> B ->
on_parallel C D A B ->
on_parallel E F C D ->
parallel A B E F.