From 4ade23ef522409d0754198ea35747a65b6fa9d81 Mon Sep 17 00:00:00 2001
From: letouzey <letouzey@85f007b7-540e-0410-9357-904b9bb8a0f7>
Date: Tue, 3 Nov 2009 08:24:32 +0000
Subject: ROrderedType + Rminmax : Coq's Reals can be seen as OrderedType. This
 way we get properties of Rmin / Rmax (almost) for free.

TODO: merge Rbasic_fun and Rminmax...

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@12463 85f007b7-540e-0410-9357-904b9bb8a0f7
---
 theories/Reals/Rminmax.v | 214 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 214 insertions(+)
 create mode 100644 theories/Reals/Rminmax.v

(limited to 'theories/Reals/Rminmax.v')

diff --git a/theories/Reals/Rminmax.v b/theories/Reals/Rminmax.v
new file mode 100644
index 000000000..70bc00c9f
--- /dev/null
+++ b/theories/Reals/Rminmax.v
@@ -0,0 +1,214 @@
+(************************************************************************)
+(*  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 OrderedType2 Rbase Rbasic_fun ROrderedType GenericMinMax.
+
+(** * Maximum and Minimum of two real numbers *)
+
+Local Open Scope R_scope.
+
+(** The functions [Rmax] and [Rmin] implement indeed
+    a maximum and a minimum *)
+
+Lemma Rmax_spec : forall x y,
+  (x<y /\ Rmax x y = y)  \/  (y<=x /\ Rmax x y = x).
+Proof.
+ unfold Rmax. intros.
+ destruct Rle_dec as [H|H]; [| apply Rnot_le_lt in H ];
+  unfold Rle in *; intuition.
+Qed.
+
+Lemma Rmin_spec : forall x y,
+  (x<y /\ Rmin x y = x)  \/  (y<=x /\ Rmin x y = y).
+Proof.
+ unfold Rmin. intros.
+ destruct Rle_dec as [H|H]; [| apply Rnot_le_lt in H ];
+  unfold Rle in *; intuition.
+Qed.
+
+Module RHasMinMax <: HasMinMax R_as_OT.
+ Definition max := Rmax.
+ Definition min := Rmin.
+ Definition max_spec := Rmax_spec.
+ Definition min_spec := Rmin_spec.
+End RHasMinMax.
+
+(** We obtain hence all the generic properties of max and min. *)
+
+Module Import RMinMaxProps := MinMaxProperties R_as_OT RHasMinMax.
+
+(** For some generic properties, we can have nicer statements here,
+    since underlying equality is Leibniz. *)
+
+Lemma Rmax_case_strong : forall n m (P:R -> Type),
+  (m<=n -> P n) -> (n<=m -> P m) -> P (Rmax n m).
+Proof. intros; apply max_case_strong; auto. congruence. Defined.
+
+Lemma Rmax_case : forall n m (P:R -> Type),
+  P n -> P m -> P (Rmax n m).
+Proof. intros. apply Rmax_case_strong; auto. Defined.
+
+Lemma Rmax_monotone: forall f,
+ (Proper (Rle ==> Rle) f) ->
+ forall x y, Rmax (f x) (f y) = f (Rmax x y).
+Proof. intros; apply max_monotone; auto. congruence. Qed.
+
+Lemma Rmin_case_strong : forall n m (P:R -> Type),
+  (m<=n -> P m) -> (n<=m -> P n) -> P (Rmin n m).
+Proof. intros; apply min_case_strong; auto. congruence. Defined.
+
+Lemma Rmin_case : forall n m (P:R -> Type),
+  P n -> P m -> P (Rmin n m).
+Proof. intros. apply Rmin_case_strong; auto. Defined.
+
+Lemma Rmin_monotone: forall f,
+ (Proper (Rle ==> Rle) f) ->
+ forall x y, Rmin (f x) (f y) = f (Rmin x y).
+Proof. intros; apply min_monotone; auto. congruence. Qed.
+
+Lemma Rmax_min_antimonotone : forall f,
+ Proper (Rle==>Rge) f ->
+ forall x y, Rmax (f x) (f y) == f (Rmin x y).
+Proof.
+ intros. apply max_min_antimonotone. congruence.
+ intros z z' Hz; red; apply Rge_le; auto.
+Qed.
+
+Lemma Rmin_max_antimonotone : forall f,
+ Proper (Rle==>Rge) f ->
+ forall x y, Rmin (f x) (f y) == f (Rmax x y).
+Proof.
+ intros. apply min_max_antimonotone. congruence.
+ intros z z' Hz; red. apply Rge_le. auto.
+Qed.
+
+(** For the other generic properties, we make aliases,
+   since otherwise SearchAbout misses some of them
+   (bad interaction with an Include).
+   See GenericMinMax (or SearchAbout) for the statements. *)
+
+Definition Rmax_spec_le := max_spec_le.
+Definition Rmax_dec := max_dec.
+Definition Rmax_unicity := max_unicity.
+Definition Rmax_unicity_ext := max_unicity_ext.
+Definition Rmax_id := max_id.
+Notation Rmax_idempotent := Rmax_id (only parsing).
+Definition Rmax_assoc := max_assoc.
+Definition Rmax_comm := max_comm.
+Definition Rmax_l := max_l.
+Definition Rmax_r := max_r.
+Definition Zle_max_l := le_max_l.
+Definition Zle_max_r := le_max_r.
+Definition Rmax_le := max_le.
+Definition Rmax_le_iff := max_le_iff.
+Definition Rmax_lt_iff := max_lt_iff.
+Definition Rmax_lub_l := max_lub_l.
+Definition Rmax_lub_r := max_lub_r.
+Definition Rmax_lub := max_lub.
+Definition Rmax_lub_iff := max_lub_iff.
+Definition Rmax_lub_lt := max_lub_lt.
+Definition Rmax_lub_lt_iff := max_lub_lt_iff.
+Definition Rmax_le_compat_l := max_le_compat_l.
+Definition Rmax_le_compat_r := max_le_compat_r.
+Definition Rmax_le_compat := max_le_compat.
+
+Definition Rmin_spec_le := min_spec_le.
+Definition Rmin_dec := min_dec.
+Definition Rmin_unicity := min_unicity.
+Definition Rmin_unicity_ext := min_unicity_ext.
+Definition Rmin_id := min_id.
+Notation Rmin_idempotent := Rmin_id (only parsing).
+Definition Rmin_assoc := min_assoc.
+Definition Rmin_comm := min_comm.
+Definition Rmin_l := min_l.
+Definition Rmin_r := min_r.
+Definition Zle_min_l := le_min_l.
+Definition Zle_min_r := le_min_r.
+Definition Rmin_le := min_le.
+Definition Rmin_le_iff := min_le_iff.
+Definition Rmin_lt_iff := min_lt_iff.
+Definition Rmin_glb_l := min_glb_l.
+Definition Rmin_glb_r := min_glb_r.
+Definition Rmin_glb := min_glb.
+Definition Rmin_glb_iff := min_glb_iff.
+Definition Rmin_glb_lt := min_glb_lt.
+Definition Rmin_glb_lt_iff := min_glb_lt_iff.
+Definition Rmin_le_compat_l := min_le_compat_l.
+Definition Rmin_le_compat_r := min_le_compat_r.
+Definition Rmin_le_compat := min_le_compat.
+
+Definition Rmin_max_absorption := min_max_absorption.
+Definition Rmax_min_absorption := max_min_absorption.
+Definition Rmax_min_distr := max_min_distr.
+Definition Rmin_max_distr := min_max_distr.
+Definition Rmax_min_modular := max_min_modular.
+Definition Rmin_max_modular := min_max_modular.
+Definition Rmax_min_disassoc := max_min_disassoc.
+
+
+(** * Properties specific to the [R] domain *)
+
+(** Compatibilities (consequences of monotonicity) *)
+
+Lemma Rplus_max_distr_l : forall n m p, Rmax (p + n) (p + m) = p + Rmax n m.
+Proof.
+ intros. apply Rmax_monotone.
+ intros x y. apply Rplus_le_compat_l.
+Qed.
+
+Lemma Rplus_max_distr_r : forall n m p, Rmax (n + p) (m + p) = Rmax n m + p.
+Proof.
+ intros. rewrite (Rplus_comm n p), (Rplus_comm m p), (Rplus_comm _ p).
+ apply Rplus_max_distr_l.
+Qed.
+
+Lemma Rplus_min_distr_l : forall n m p, Rmin (p + n) (p + m) = p + Rmin n m.
+Proof.
+ intros. apply Rmin_monotone.
+ intros x y. apply Rplus_le_compat_l.
+Qed.
+
+Lemma Rplus_min_distr_r : forall n m p, Rmin (n + p) (m + p) = Rmin n m + p.
+Proof.
+ intros. rewrite (Rplus_comm n p), (Rplus_comm m p), (Rplus_comm _ p).
+ apply Rplus_min_distr_l.
+Qed.
+
+(** Anti-monotonicity swaps the role of [min] and [max] *)
+
+Lemma Ropp_max_distr : forall n m : R, -(Rmax n m) = Rmin (- n) (- m).
+Proof.
+ intros. symmetry. apply Rmin_max_antimonotone.
+ exact Ropp_le_ge_contravar.
+Qed.
+
+Lemma Ropp_min_distr : forall n m : R, - (Rmin n m) = Rmax (- n) (- m).
+Proof.
+ intros. symmetry. apply Rmax_min_antimonotone.
+ exact Ropp_le_ge_contravar.
+Qed.
+
+Lemma Rminus_max_distr_l : forall n m p, Rmax (p - n) (p - m) = p - Rmin n m.
+Proof.
+ unfold Rminus. intros. rewrite Ropp_min_distr. apply Rplus_max_distr_l.
+Qed.
+
+Lemma Rminus_max_distr_r : forall n m p, Rmax (n - p) (m - p) = Rmax n m - p.
+Proof.
+ unfold Rminus. intros. apply Rplus_max_distr_r.
+Qed.
+
+Lemma Rminus_min_distr_l : forall n m p, Rmin (p - n) (p - m) = p - Rmax n m.
+Proof.
+ unfold Rminus. intros. rewrite Ropp_max_distr. apply Rplus_min_distr_l.
+Qed.
+
+Lemma Rminus_min_distr_r : forall n m p, Rmin (n - p) (m - p) = Rmin n m - p.
+Proof.
+ unfold Rminus. intros. apply Rplus_min_distr_r.
+Qed.
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