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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 line going through the midpoints is parallel to the third side *)

Theorem th6_7 :
forall A B C L M N O : Point,
inter_ll L B C A O ->
inter_ll N B A C O ->
inter_ll M A C B O ->
S A M L * (S B N M * S C L N) = S A N L * (S B L M * S C N M).