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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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Theorem example6_9 : forall L M N A B C SS:Point,
parallel A M M C ->
parallel A N N B ->
parallel A SS SS L ->
M<>C ->
N<>B ->
SS<>L ->
inter_ll L B C A SS ->
inter_ll N B A C SS ->
inter_ll M A C B SS ->
A**M/M**C+A**N/N**B = A**SS/SS**L.