From 5db31bb0333810ccdd0a79e9855ae9d2fcdbf2d3 Mon Sep 17 00:00:00 2001
From: letouzey
Date: Fri, 8 Jan 2010 14:44:56 +0000
Subject: Numbers: axiomatization + generic properties of abs and sgn.

 This allow to really finish files about division.
 An abs and sgn is added to BigZ.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@12644 85f007b7-540e-0410-9357-904b9bb8a0f7
---
 theories/Numbers/Integer/SpecViaZ/ZSig.v        |  8 ++++++
 theories/Numbers/Integer/SpecViaZ/ZSigZAxioms.v | 38 ++++++++++++++++++++++---
 2 files changed, 42 insertions(+), 4 deletions(-)

(limited to 'theories/Numbers/Integer/SpecViaZ')

diff --git a/theories/Numbers/Integer/SpecViaZ/ZSig.v b/theories/Numbers/Integer/SpecViaZ/ZSig.v
index 00e292db0f..ef3cd5c341 100644
--- a/theories/Numbers/Integer/SpecViaZ/ZSig.v
+++ b/theories/Numbers/Integer/SpecViaZ/ZSig.v
@@ -114,4 +114,12 @@ Module Type ZType.
 
  Parameter spec_gcd: forall a b, [gcd a b] = Zgcd (to_Z a) (to_Z b).
 
+ Parameter sgn : t -> t.
+
+ Parameter spec_sgn : forall x, [sgn x] = Zsgn [x].
+
+ Parameter abs : t -> t.
+
+ Parameter spec_abs : forall x, [abs x] = Zabs [x].
+
 End ZType.
diff --git a/theories/Numbers/Integer/SpecViaZ/ZSigZAxioms.v b/theories/Numbers/Integer/SpecViaZ/ZSigZAxioms.v
index 666ce5454f..80166d5bf2 100644
--- a/theories/Numbers/Integer/SpecViaZ/ZSigZAxioms.v
+++ b/theories/Numbers/Integer/SpecViaZ/ZSigZAxioms.v
@@ -8,13 +8,11 @@
 
 (*i $Id$ i*)
 
-Require Import ZArith.
-Require Import ZAxioms.
-Require Import ZSig.
+Require Import ZArith ZAxioms ZSgnAbs ZSig.
 
 (** * The interface [ZSig.ZType] implies the interface [ZAxiomsSig] *)
 
-Module ZSig_ZAxioms (Z:ZType) <: ZAxiomsSig.
+Module ZSig_ZAxioms (Z:ZType) <: ZAxiomsExtSig.
 
 Local Notation "[ x ]" := (Z.to_Z x).
 Local Infix "=="  := Z.eq (at level 70).
@@ -235,6 +233,36 @@ Proof.
 intros; zsimpl; auto with zarith.
 Qed.
 
+Theorem abs_eq : forall n, 0 <= n -> Z.abs n == n.
+Proof.
+intros. red. rewrite Z.spec_abs. apply Zabs_eq.
+ rewrite <- Z.spec_0, <- spec_le; auto.
+Qed.
+
+Theorem abs_neq : forall n, n <= 0 -> Z.abs n == -n.
+Proof.
+intros. red. rewrite Z.spec_abs, Z.spec_opp. apply Zabs_non_eq.
+ rewrite <- Z.spec_0, <- spec_le; auto.
+Qed.
+
+Theorem sgn_null : forall n, n==0 -> Z.sgn n == 0.
+Proof.
+intros. red. rewrite Z.spec_sgn, Z.spec_0. rewrite Zsgn_null.
+ rewrite <- Z.spec_0; auto.
+Qed.
+
+Theorem sgn_pos : forall n, 0<n -> Z.sgn n == Z.succ 0.
+Proof.
+intros. red. rewrite Z.spec_sgn. zsimpl. rewrite Zsgn_pos.
+ rewrite <- Z.spec_0, <- spec_lt; auto.
+Qed.
+
+Theorem sgn_neg : forall n, n<0 -> Z.sgn n == Z.opp (Z.succ 0).
+Proof.
+intros. red. rewrite Z.spec_sgn. zsimpl. rewrite Zsgn_neg.
+ rewrite <- Z.spec_0, <- spec_lt; auto.
+Qed.
+
 (** Aliases *)
 
 Definition t := Z.t.
@@ -250,5 +278,7 @@ Definition lt := Z.lt.
 Definition le := Z.le.
 Definition min := Z.min.
 Definition max := Z.max.
+Definition abs := Z.abs.
+Definition sgn := Z.sgn.
 
 End ZSig_ZAxioms.
-- 
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