diff options
Diffstat (limited to 'theories/Init/Peano.v')
| -rw-r--r-- | theories/Init/Peano.v | 96 |
1 files changed, 85 insertions, 11 deletions
diff --git a/theories/Init/Peano.v b/theories/Init/Peano.v index abf843bf..c3716eaa 100644 --- a/theories/Init/Peano.v +++ b/theories/Init/Peano.v @@ -1,13 +1,11 @@ (************************************************************************) (* v * The Coq Proof Assistant / The Coq Development Team *) -(* <O___,, * INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2011 *) +(* <O___,, * INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2010 *) (* \VV/ **************************************************************) (* // * This file is distributed under the terms of the *) (* * GNU Lesser General Public License Version 2.1 *) (************************************************************************) -(*i $Id: Peano.v 14641 2011-11-06 11:59:10Z herbelin $ i*) - (** The type [nat] of Peano natural numbers (built from [O] and [S]) is defined in [Datatypes.v] *) @@ -28,7 +26,6 @@ Require Import Notations. Require Import Datatypes. Require Import Logic. -Unset Boxed Definitions. Open Scope nat_scope. @@ -52,13 +49,7 @@ Qed. (** Injectivity of successor *) -Theorem eq_add_S : forall n m:nat, S n = S m -> n = m. -Proof. - intros n m Sn_eq_Sm. - replace (n=m) with (pred (S n) = pred (S m)) by auto using pred_Sn. - rewrite Sn_eq_Sm; trivial. -Qed. - +Definition eq_add_S n m (H: S n = S m): n = m := f_equal pred H. Hint Immediate eq_add_S: core. Theorem not_eq_S : forall n m:nat, n <> m -> S n <> S m. @@ -201,6 +192,16 @@ Notation "x <= y < z" := (x <= y /\ y < z) : nat_scope. Notation "x < y < z" := (x < y /\ y < z) : nat_scope. Notation "x < y <= z" := (x < y /\ y <= z) : nat_scope. +Theorem le_pred : forall n m, n <= m -> pred n <= pred m. +Proof. +induction 1; auto. destruct m; simpl; auto. +Qed. + +Theorem le_S_n : forall n m, S n <= S m -> n <= m. +Proof. +intros n m. exact (le_pred (S n) (S m)). +Qed. + (** Case analysis *) Theorem nat_case : @@ -220,3 +221,76 @@ Proof. induction n; auto. destruct m as [| n0]; auto. Qed. + +(** Maximum and minimum : definitions and specifications *) + +Fixpoint max n m : nat := + match n, m with + | O, _ => m + | S n', O => n + | S n', S m' => S (max n' m') + end. + +Fixpoint min n m : nat := + match n, m with + | O, _ => 0 + | S n', O => 0 + | S n', S m' => S (min n' m') + end. + +Theorem max_l : forall n m : nat, m <= n -> max n m = n. +Proof. +induction n; destruct m; simpl; auto. inversion 1. +intros. apply f_equal. apply IHn. apply le_S_n. trivial. +Qed. + +Theorem max_r : forall n m : nat, n <= m -> max n m = m. +Proof. +induction n; destruct m; simpl; auto. inversion 1. +intros. apply f_equal. apply IHn. apply le_S_n. trivial. +Qed. + +Theorem min_l : forall n m : nat, n <= m -> min n m = n. +Proof. +induction n; destruct m; simpl; auto. inversion 1. +intros. apply f_equal. apply IHn. apply le_S_n. trivial. +Qed. + +Theorem min_r : forall n m : nat, m <= n -> min n m = m. +Proof. +induction n; destruct m; simpl; auto. inversion 1. +intros. apply f_equal. apply IHn. apply le_S_n. trivial. +Qed. + +(** [n]th iteration of the function [f] *) + +Fixpoint nat_iter (n:nat) {A} (f:A->A) (x:A) : A := + match n with + | O => x + | S n' => f (nat_iter n' f x) + end. + +Lemma nat_iter_succ_r n {A} (f:A->A) (x:A) : + nat_iter (S n) f x = nat_iter n f (f x). +Proof. + induction n; intros; simpl; rewrite <- ?IHn; trivial. +Qed. + +Theorem nat_iter_plus : + forall (n m:nat) {A} (f:A -> A) (x:A), + nat_iter (n + m) f x = nat_iter n f (nat_iter m f x). +Proof. + induction n; intros; simpl; rewrite ?IHn; trivial. +Qed. + +(** Preservation of invariants : if [f : A->A] preserves the invariant [Inv], + then the iterates of [f] also preserve it. *) + +Theorem nat_iter_invariant : + forall (n:nat) {A} (f:A -> A) (P : A -> Prop), + (forall x, P x -> P (f x)) -> + forall x, P x -> P (nat_iter n f x). +Proof. + induction n; simpl; trivial. + intros A f P Hf x Hx. apply Hf, IHn; trivial. +Qed. |