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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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(** Area elimination *)
(** on_line *)
(** on_line_d *)
(* inter_ll *)
(* on_foot *)

Lemma test_area_on_foot_1  : forall I X Y Z A B,
on_foot I X Y Z -> S A B I = (Py X Y Z * S A B Z + Py X Z Y * S A B Y) / (Py Y Z Y).