Numbers: properties of min/max with respect to 0,S,P,add,sub,mul

 With these properties, we can kill Arith/MinMax, NArith/Nminmax,
 and leave ZArith/Zminmax as a compatibility file only. Now
 the instanciations NPeano.Nat, NBinary.N, ZBinary.Z, BigZ, BigN
 contains all theses facts.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@12718 85f007b7-540e-0410-9357-904b9bb8a0f7

3 files changed, 149 insertions, 3 deletions

diff --git a/theories/Numbers/Natural/Abstract/NMaxMin.v b/theories/Numbers/Natural/Abstract/NMaxMin.v
new file mode 100644
index 0000000000..9406bce221
--- /dev/null
+++ b/theories/Numbers/Natural/Abstract/NMaxMin.v
@@ -0,0 +1,135 @@
+(************************************************************************)
+(*  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        *)
+(************************************************************************)
+
+Require Import NAxioms NSub GenericMinMax.
+
+(** * Properties of minimum and maximum specific to natural numbers *)
+
+Module Type NMaxMinProp (Import N : NAxiomsSig').
+Include NSubPropFunct N.
+
+(** Zero *)
+
+Lemma max_0_l : forall n, max 0 n == n.
+Proof.
+ intros. apply max_r. apply le_0_l.
+Qed.
+
+Lemma max_0_r : forall n, max n 0 == n.
+Proof.
+ intros. apply max_l. apply le_0_l.
+Qed.
+
+Lemma min_0_l : forall n, min 0 n == 0.
+Proof.
+ intros. apply min_l. apply le_0_l.
+Qed.
+
+Lemma min_0_r : forall n, min n 0 == 0.
+Proof.
+ intros. apply min_r. apply le_0_l.
+Qed.
+
+(** The following results are concrete instances of [max_monotone]
+    and similar lemmas. *)
+
+(** Succ *)
+
+Lemma succ_max_distr : forall n m, S (max n m) == max (S n) (S m).
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 max_r | rewrite 2 max_l]; now rewrite <- ?succ_le_mono.
+Qed.
+
+Lemma succ_min_distr : forall n m, S (min n m) == min (S n) (S m).
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 min_l | rewrite 2 min_r]; now rewrite <- ?succ_le_mono.
+Qed.
+
+(** Add *)
+
+Lemma add_max_distr_l : forall n m p, max (p + n) (p + m) == p + max n m.
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 max_r | rewrite 2 max_l]; now rewrite <- ?add_le_mono_l.
+Qed.
+
+Lemma add_max_distr_r : forall n m p, max (n + p) (m + p) == max n m + p.
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 max_r | rewrite 2 max_l]; now rewrite <- ?add_le_mono_r.
+Qed.
+
+Lemma add_min_distr_l : forall n m p, min (p + n) (p + m) == p + min n m.
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 min_l | rewrite 2 min_r]; now rewrite <- ?add_le_mono_l.
+Qed.
+
+Lemma add_min_distr_r : forall n m p, min (n + p) (m + p) == min n m + p.
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 min_l | rewrite 2 min_r]; now rewrite <- ?add_le_mono_r.
+Qed.
+
+(** Mul *)
+
+Lemma mul_max_distr_l : forall n m p, max (p * n) (p * m) == p * max n m.
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 max_r | rewrite 2 max_l]; try order; now apply mul_le_mono_l.
+Qed.
+
+Lemma mul_max_distr_r : forall n m p, max (n * p) (m * p) == max n m * p.
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 max_r | rewrite 2 max_l]; try order; now apply mul_le_mono_r.
+Qed.
+
+Lemma mul_min_distr_l : forall n m p, min (p * n) (p * m) == p * min n m.
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 min_l | rewrite 2 min_r]; try order; now apply mul_le_mono_l.
+Qed.
+
+Lemma mul_min_distr_r : forall n m p, min (n * p) (m * p) == min n m * p.
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 min_l | rewrite 2 min_r]; try order; now apply mul_le_mono_r.
+Qed.
+
+(** Sub *)
+
+Lemma sub_max_distr_l : forall n m p, max (p - n) (p - m) == p - min n m.
+Proof.
+ intros. destruct (le_ge_cases n m).
+ rewrite min_l by trivial. apply max_l. now apply sub_le_mono_l.
+ rewrite min_r by trivial. apply max_r. now apply sub_le_mono_l.
+Qed.
+
+Lemma sub_max_distr_r : forall n m p, max (n - p) (m - p) == max n m - p.
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 max_r | rewrite 2 max_l]; try order; now apply sub_le_mono_r.
+Qed.
+
+Lemma sub_min_distr_l : forall n m p, min (p - n) (p - m) == p - max n m.
+Proof.
+ intros. destruct (le_ge_cases n m).
+ rewrite max_r by trivial. apply min_r. now apply sub_le_mono_l.
+ rewrite max_l by trivial. apply min_l. now apply sub_le_mono_l.
+Qed.
+
+Lemma sub_min_distr_r : forall n m p, min (n - p) (m - p) == min n m - p.
+Proof.
+ intros. destruct (le_ge_cases n m);
+  [rewrite 2 min_l | rewrite 2 min_r]; try order; now apply sub_le_mono_r.
+Qed.
+
+End NMaxMinProp.
diff --git a/theories/Numbers/Natural/Abstract/NProperties.v b/theories/Numbers/Natural/Abstract/NProperties.v
index 30262bd9f4..9fc9b290e5 100644
--- a/theories/Numbers/Natural/Abstract/NProperties.v
+++ b/theories/Numbers/Natural/Abstract/NProperties.v
@@ -8,14 +8,14 @@
 
 (*i $Id$ i*)
 
-Require Export NAxioms NSub.
+Require Export NAxioms NMaxMin.
 
 (** This functor summarizes all known facts about N.
-    For the moment it is only an alias to [NSubPropFunct], which
+    For the moment it is only an alias to the last functor which
     subsumes all others.
 *)
 
-Module Type NPropSig := NSubPropFunct.
+Module Type NPropSig := NMaxMinProp.
 
 Module NPropFunct (N:NAxiomsSig) <: NPropSig N.
  Include NPropSig N.
diff --git a/theories/Numbers/Natural/Abstract/NSub.v b/theories/Numbers/Natural/Abstract/NSub.v
index de0c2da1b0..1df032ea35 100644
--- a/theories/Numbers/Natural/Abstract/NSub.v
+++ b/theories/Numbers/Natural/Abstract/NSub.v
@@ -214,6 +214,17 @@ apply add_sub_eq_nz in EQ; [|order].
 rewrite (add_lt_mono_r _ _ n), add_0_l in LT. order.
 Qed.
 
+Lemma sub_le_mono_r : forall n m p, n <= m -> n-p <= m-p.
+Proof.
+ intros. rewrite le_sub_le_add_r. transitivity m. assumption. apply sub_add_le.
+Qed.
+
+Lemma sub_le_mono_l : forall n m p, n <= m -> p-m <= p-n.
+Proof.
+ intros. rewrite le_sub_le_add_r.
+ transitivity (p-n+n); [ apply sub_add_le | now apply add_le_mono_l].
+Qed.
+
 (** Sub and mul *)
 
 Theorem mul_pred_r : forall n m, n * (P m) == n * m - n.