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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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Require Export advanced_parallel_lemmas.
Require Export geometry_tools.
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(*  Elimination Theorems                                               *)
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(* Area elimination *)
unfold on_line in |- *.

Theorem non_zero_denom_inter_ll_area :
forall A B C D E : Point, inter_ll A B C D E -> S4 B D C E <> 0.