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+(************************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
+(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *)
+(*   \VV/  **************************************************************)
+(*    //   *      This file is distributed under the terms of the       *)
+(*         *       GNU Lesser General Public License Version 2.1        *)
+(************************************************************************)
+
+(*i $Id: Qring.v 8883 2006-05-31 21:56:37Z letouzey $ i*)
+
+Require Import Ring.
+Require Export Setoid_ring.
+Require Export QArith_base.
+
+(** * A ring tactic for rational numbers *)
+
+Definition Qeq_bool (x y : Q) :=
+  if Qeq_dec x y then true else false.
+
+Lemma Qeq_bool_correct : forall x y : Q, Qeq_bool x y = true -> x==y.
+intros x y; unfold Qeq_bool in |- *; case (Qeq_dec x y); simpl in |- *; auto.
+intros _ H; inversion H.
+Qed.
+
+Definition Qsrt : Setoid_Ring_Theory Qeq Qplus Qmult 1 0 Qopp Qeq_bool.
+Proof.
+constructor.
+exact Qplus_comm.
+exact Qplus_assoc.
+exact Qmult_comm.
+exact Qmult_assoc.
+exact Qplus_0_l.
+exact Qmult_1_l.
+exact Qplus_opp_r.
+exact Qmult_plus_distr_l.
+unfold Is_true; intros x y; generalize (Qeq_bool_correct x y);
+ case (Qeq_bool x y); auto.
+Qed.
+
+Add Setoid Ring Q Qeq Q_Setoid Qplus Qmult 1 0 Qopp Qeq_bool
+ Qplus_comp Qmult_comp Qopp_comp Qsrt
+ [ Qmake (*inject_Z*)  Zpos 0%Z Zneg xI xO 1%positive ].
+
+(** Exemple of use: *)
+
+Section Examples. 
+
+Let ex1 : forall x y z : Q, (x+y)*z ==  (x*z)+(y*z).
+intros.
+ring.
+Qed.
+
+Let ex2 : forall x y : Q, x+y == y+x.
+intros. 
+ring.
+Qed.
+
+Let ex3 : forall x y z : Q, (x+y)+z == x+(y+z).
+intros.
+ring.
+Qed.
+
+Let ex4 : (inject_Z 1)+(inject_Z 1)==(inject_Z 2).
+ring.
+Qed.
+
+Let ex5 : 1+1 == 2#1.
+ring.
+Qed.
+
+Let ex6 : (1#1)+(1#1) == 2#1.
+ring.
+Qed.
+
+Let ex7 : forall x : Q, x-x== 0#1.
+intro.
+ring.
+Qed.
+
+End Examples.
+
+Lemma Qopp_plus : forall a b,  -(a+b) == -a + -b.
+Proof.
+intros; ring.
+Qed.
+
+Lemma Qopp_opp : forall q, - -q==q.
+Proof.
+intros; ring.
+Qed.
+