From 2a7a989025a5dde9a6f34792e1e1f2b4e3ad3108 Mon Sep 17 00:00:00 2001 From: letouzey Date: Tue, 2 Nov 2010 19:30:57 +0000 Subject: Add small utility lemmas about nat/P/Z/Q arithmetic. Initial patch by Eelis van der Weegen, minor adaptations by myself git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@13613 85f007b7-540e-0410-9357-904b9bb8a0f7 --- theories/QArith/QArith_base.v | 159 ++++++++++++++++++++++++++++++++++++++++++ theories/QArith/Qabs.v | 35 ++++++++++ theories/QArith/Qround.v | 13 +++- 3 files changed, 206 insertions(+), 1 deletion(-) (limited to 'theories/QArith') diff --git a/theories/QArith/QArith_base.v b/theories/QArith/QArith_base.v index b07d3d512..fe37fccb8 100644 --- a/theories/QArith/QArith_base.v +++ b/theories/QArith/QArith_base.v @@ -46,6 +46,13 @@ Notation "x > y" := (Qlt y x)(only parsing) : Q_scope. Notation "x >= y" := (Qle y x)(only parsing) : Q_scope. Notation "x <= y <= z" := (x<=y/\y<=z) : Q_scope. +(** injection from Z is injective. *) + +Lemma inject_Z_injective (a b: Z): inject_Z a == inject_Z b <-> a = b. +Proof. + unfold Qeq. simpl. omega. +Qed. + (** Another approach : using Qcompare for defining order relations. *) Definition Qcompare (p q : Q) := (Qnum p * QDen q ?= Qnum q * QDen p)%Z. @@ -385,6 +392,26 @@ Proof. red; simpl; intro; ring. Qed. +(** Injectivity of addition (uses theory about Qopp above): *) + +Lemma Qplus_inj_r (x y z: Q): + x + z == y + z <-> x == y. +Proof. + split; intro E. + rewrite <- (Qplus_0_r x), <- (Qplus_0_r y). + rewrite <- (Qplus_opp_r z); auto. + do 2 rewrite Qplus_assoc. + rewrite E. reflexivity. + rewrite E. reflexivity. +Qed. + +Lemma Qplus_inj_l (x y z: Q): + z + x == z + y <-> x == y. +Proof. + rewrite (Qplus_comm z x), (Qplus_comm z y). + apply Qplus_inj_r. +Qed. + (** * Properties of [Qmult] *) @@ -460,6 +487,21 @@ Proof. rewrite <- H0; ring. Qed. + +(** * inject_Z is a ring homomorphism: *) + +Lemma inject_Z_plus (x y: Z): inject_Z (x + y) = inject_Z x + inject_Z y. +Proof. + unfold Qplus, inject_Z. simpl. f_equal. ring. +Qed. + +Lemma inject_Z_mult (x y: Z): inject_Z (x * y) = inject_Z x * inject_Z y. +Proof. reflexivity. Qed. + +Lemma inject_Z_opp (x: Z): inject_Z (- x) = - inject_Z x. +Proof. reflexivity. Qed. + + (** * Inverse and division. *) Lemma Qinv_involutive : forall q, (/ / q) == q. @@ -498,6 +540,25 @@ Proof. apply Qdiv_mult_l; auto. Qed. +(** Injectivity of Qmult (requires theory about Qinv above): *) + +Lemma Qmult_inj_r (x y z: Q): ~ z == 0 -> (x * z == y * z <-> x == y). +Proof. + intro z_ne_0. + split; intro E. + rewrite <- (Qmult_1_r x), <- (Qmult_1_r y). + rewrite <- (Qmult_inv_r z); auto. + do 2 rewrite Qmult_assoc. + rewrite E. reflexivity. + rewrite E. reflexivity. +Qed. + +Lemma Qmult_inj_l (x y z: Q): ~ z == 0 -> (z * x == z * y <-> x == y). +Proof. + rewrite (Qmult_comm z x), (Qmult_comm z y). + apply Qmult_inj_r. +Qed. + (** * Properties of order upon Q. *) Lemma Qle_refl : forall x, x<=x. @@ -537,6 +598,19 @@ Proof. unfold Qlt, Qeq; auto with zarith. Qed. +Lemma Zle_Qle (x y: Z): (x <= y)%Z = (inject_Z x <= inject_Z y). +Proof. + unfold Qle. intros. simpl. + do 2 rewrite Zmult_1_r. reflexivity. +Qed. + +Lemma Zlt_Qlt (x y: Z): (x < y)%Z = (inject_Z x < inject_Z y). +Proof. + unfold Qlt. intros. simpl. + do 2 rewrite Zmult_1_r. reflexivity. +Qed. + + (** Large = strict or equal *) Lemma Qle_lteq : forall x y, x<=y <-> x z<=t -> x+z < y+t. +Proof. + unfold Qplus, Qle, Qlt; intros (x1, x2) (y1, y2) (z1, z2) (t1, t2); + simpl; simpl_mult. + Open Scope Z_scope. + intros. + match goal with |- ?a < ?b => ring_simplify a b end. + rewrite Zplus_comm. + apply Zplus_le_lt_compat. + match goal with |- ?a <= ?b => ring_simplify z1 t1 ('z2) ('t2) a b end. + auto with zarith. + match goal with |- ?a < ?b => ring_simplify x1 y1 ('x2) ('y2) a b end. + assert (forall p, 0 < ' p) by reflexivity. + repeat (apply Zmult_lt_compat_r; auto). + Close Scope Z_scope. +Qed. + +Lemma Qplus_le_l (x y z: Q): x + z <= y + z <-> x <= y. +Proof. + split; intros. + rewrite <- (Qplus_0_r x), <- (Qplus_0_r y), <- (Qplus_opp_r z). + do 2 rewrite Qplus_assoc. + apply Qplus_le_compat; auto with *. + apply Qplus_le_compat; auto with *. +Qed. + +Lemma Qplus_le_r (x y z: Q): z + x <= z + y <-> x <= y. +Proof. + rewrite (Qplus_comm z x), (Qplus_comm z y). + apply Qplus_le_l. +Qed. + +Lemma Qplus_lt_l (x y z: Q): x + z < y + z <-> x < y. +Proof. + split; intros. + rewrite <- (Qplus_0_r x), <- (Qplus_0_r y), <- (Qplus_opp_r z). + do 2 rewrite Qplus_assoc. + apply Qplus_lt_le_compat; auto with *. + apply Qplus_lt_le_compat; auto with *. +Qed. + +Lemma Qplus_lt_r (x y z: Q): z + x < z + y <-> x < y. +Proof. + rewrite (Qplus_comm z x), (Qplus_comm z y). + apply Qplus_lt_l. +Qed. + Lemma Qmult_le_compat_r : forall x y z, x <= y -> 0 <= z -> x*z <= y*z. Proof. intros (a1,a2) (b1,b2) (c1,c2); unfold Qle, Qlt; simpl. @@ -697,6 +819,19 @@ Proof. Close Scope Z_scope. Qed. +Lemma Qmult_le_r (x y z: Q): 0 < z -> (x*z <= y*z <-> x <= y). +Proof. + split; intro. + now apply Qmult_lt_0_le_reg_r with z. + apply Qmult_le_compat_r; auto with qarith. +Qed. + +Lemma Qmult_le_l (x y z: Q): 0 < z -> (z*x <= z*y <-> x <= y). +Proof. + rewrite (Qmult_comm z x), (Qmult_comm z y). + apply Qmult_le_r. +Qed. + Lemma Qmult_lt_compat_r : forall x y z, 0 < z -> x < y -> x*z < y*z. Proof. intros (a1,a2) (b1,b2) (c1,c2); unfold Qle, Qlt; simpl. @@ -711,6 +846,30 @@ Proof. Close Scope Z_scope. Qed. +Lemma Qmult_lt_r: forall x y z, 0 < z -> (x*z < y*z <-> x < y). +Proof. + Open Scope Z_scope. + intros (a1,a2) (b1,b2) (c1,c2). + unfold Qle, Qlt; simpl. + simpl_mult. + replace (a1*c1*('b2*'c2)) with ((a1*'b2)*(c1*'c2)) by ring. + replace (b1*c1*('a2*'c2)) with ((b1*'a2)*(c1*'c2)) by ring. + assert (forall p, 0 < ' p) by reflexivity. + split; intros. + apply Zmult_lt_reg_r with (c1*'c2); auto with zarith. + apply Zmult_lt_0_compat; auto with zarith. + apply Zmult_lt_compat_r; auto with zarith. + apply Zmult_lt_0_compat. omega. + compute; auto. + Close Scope Z_scope. +Qed. + +Lemma Qmult_lt_l (x y z: Q): 0 < z -> (z*x < z*y <-> x < y). +Proof. + rewrite (Qmult_comm z x), (Qmult_comm z y). + apply Qmult_lt_r. +Qed. + Lemma Qmult_le_0_compat : forall a b, 0 <= a -> 0 <= b -> 0 <= a*b. Proof. intros a b Ha Hb. diff --git a/theories/QArith/Qabs.v b/theories/QArith/Qabs.v index 53528ec74..557fabc89 100644 --- a/theories/QArith/Qabs.v +++ b/theories/QArith/Qabs.v @@ -100,6 +100,13 @@ rewrite Zabs_Zmult. reflexivity. Qed. +Lemma Qabs_Qminus x y: Qabs (x - y) = Qabs (y - x). +Proof. + unfold Qminus, Qopp. simpl. + rewrite Pmult_comm, <- Zabs_Zopp. + do 2 f_equal. ring. +Qed. + Lemma Qle_Qabs : forall a, a <= Qabs a. Proof. intros a. @@ -122,3 +129,31 @@ apply Qabs_triangle. apply Qabs_wd. ring. Qed. + +Lemma Qabs_Qle_condition x y: Qabs x <= y <-> -y <= x <= y. +Proof. + split. + split. + rewrite <- (Qopp_opp x). + apply Qopp_le_compat. + apply Qle_trans with (Qabs (-x)). + apply Qle_Qabs. + now rewrite Qabs_opp. + apply Qle_trans with (Qabs x); auto using Qle_Qabs. + intros (H,H'). + apply Qabs_case; trivial. + intros. rewrite <- (Qopp_opp y). now apply Qopp_le_compat. +Qed. + +Lemma Qabs_diff_Qle_condition x y r: Qabs (x - y) <= r <-> x - r <= y <= x + r. +Proof. + intros. unfold Qminus. + rewrite Qabs_Qle_condition. + rewrite <- (Qplus_le_l (-r) (x+-y) (y+r)). + rewrite <- (Qplus_le_l (x+-y) r (y-r)). + setoid_replace (-r + (y + r)) with y by ring. + setoid_replace (r + (y - r)) with y by ring. + setoid_replace (x + - y + (y + r)) with (x + r) by ring. + setoid_replace (x + - y + (y - r)) with (x - r) by ring. + intuition. +Qed. diff --git a/theories/QArith/Qround.v b/theories/QArith/Qround.v index 58a7967ed..ce363a33b 100644 --- a/theories/QArith/Qround.v +++ b/theories/QArith/Qround.v @@ -136,4 +136,15 @@ intros x y H. apply Zle_antisym. auto with *. symmetry in H; auto with *. -Qed. \ No newline at end of file +Qed. + +Lemma Zdiv_Qdiv (n m: Z): (n / m)%Z = Qfloor (n / m). +Proof. + unfold Qfloor. intros. simpl. + destruct m as [?|?|p]; simpl. + now rewrite Zdiv_0_r, Zmult_0_r. + now rewrite Zmult_1_r. + rewrite <- Zopp_eq_mult_neg_1. + rewrite <- (Zopp_involutive (Zpos p)). + now rewrite Zdiv_opp_opp. +Qed. -- cgit v1.2.3