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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 field_general_properties.
Require Export chou_gao_zhang_axioms.
(* This file contains the lemmas needed by the tactics used as tools for both the development and the decision procedure. *)
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(* Signed areas                                         *)
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auto with Geom.
Qed.
auto with Geom.
Qed.
Hint Resolve S_1: Geom.
Proof with try solve [ Geometry | congruence ].
intros...
assert (S A B C = - S B A C)...
assert (S B A C = S C B A)...
Qed.
Hint Resolve S_2: Geom.
Proof with try solve [ Geometry | congruence ].
intros...
assert (S A B C = - S B A C)...
assert (S B A C = S A C B)...
Qed.
Hint Resolve S_3: Geom.
intros.
Geometry.
Qed.
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(* Signed areas (4)                                     *)
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Proof with try solve [ Geometry | ring ].
intros...
unfold S4 in |- *...
assert (S A B C = S A B D + S A D C + S D B C)...
assert (S D B C = - S C B D)...
rewrite H0 in H...
assert (S A D C = - S A C D)...
rewrite H1 in H...
clear H0 H1...
rewrite H...
Qed.
Hint Resolve S4_1: Geom.

Lemma S4_2 : forall A B C D : Point, S4 A B C D = S4 B C D A.