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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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(** The Pappus line theorem *)

(* Specifications: *)
Theorem Pappus : forall A B C A' B' C' P Q R :Point,
on_line C A B ->
on_line C' A' B' ->
inter_ll P A' B A B' ->
inter_ll Q A C' A' C ->
inter_ll R B' C B C' ->
Col P Q R.