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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 *)
(** Pseudo-transitivity of the parallel predicate expressed constructively *)
(** If AB and CD are two parallel and congruent segments then AC is parallel to BD *)

Theorem parallellogram_second_parallel :
forall A B C D : Point,
on_parallel_d D C A B 1 ->
parallel A C B D.