(***************************************************************************)
(* Formalization of the Chou, Gao and Zhang's decision procedure.          *)
(* Julien Narboux (Julien@narboux.fr)                                      *)
(* LIX/INRIA FUTURS 2004-2006                                              *)
(* University of Strasbourg 2008                                           *)
(***************************************************************************)
Require Export pythagoras_difference_lemmas.
Require Export euclidean_constructions_2.
Require Export construction_lemmas_2.
Require Export ratios_elimination_lemmas.
Ltac construct_grid O U V H :=
elim grid_existence;let H:= fresh in (
intros O H; elim H; clear H;intros U H;elim H;clear H;intro V;intros H;decompose [and] H).

Lemma py_to_pys : forall A B C,
Py A B C = 1/2 * (Py A B A + Py B C B - Py A C A).