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Diffstat (limited to 'theories/Reals/Abstract/ConstructiveAbs.v')
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diff --git a/theories/Reals/Abstract/ConstructiveAbs.v b/theories/Reals/Abstract/ConstructiveAbs.v new file mode 100644 index 0000000000..d357ad2d54 --- /dev/null +++ b/theories/Reals/Abstract/ConstructiveAbs.v @@ -0,0 +1,950 @@ +(************************************************************************) +(* * The Coq Proof Assistant / The Coq Development Team *) +(* v * INRIA, CNRS and contributors - Copyright 1999-2019 *) +(* <O___,, * (see CREDITS file for the list of authors) *) +(* \VV/ **************************************************************) +(* // * This file is distributed under the terms of the *) +(* * GNU Lesser General Public License Version 2.1 *) +(* * (see LICENSE file for the text of the license) *) +(************************************************************************) +(************************************************************************) + +Require Import QArith. +Require Import Qabs. +Require Import ConstructiveReals. + +Local Open Scope ConstructiveReals. + +(** Properties of constructive absolute value (defined in + ConstructiveReals.CRabs). + Definition of minimum, maximum and their properties. *) + +Instance CRabs_morph + : forall {R : ConstructiveReals}, + CMorphisms.Proper + (CMorphisms.respectful (CReq R) (CReq R)) (CRabs R). +Proof. + intros R x y [H H0]. split. + - rewrite <- CRabs_def. split. + + apply (CRle_trans _ x). apply H. + pose proof (CRabs_def R x (CRabs R x)) as [_ H1]. + apply H1. apply CRle_refl. + + apply (CRle_trans _ (CRopp R x)). intro abs. + apply CRopp_lt_cancel in abs. contradiction. + pose proof (CRabs_def R x (CRabs R x)) as [_ H1]. + apply H1. apply CRle_refl. + - rewrite <- CRabs_def. split. + + apply (CRle_trans _ y). apply H0. + pose proof (CRabs_def R y (CRabs R y)) as [_ H1]. + apply H1. apply CRle_refl. + + apply (CRle_trans _ (CRopp R y)). intro abs. + apply CRopp_lt_cancel in abs. contradiction. + pose proof (CRabs_def R y (CRabs R y)) as [_ H1]. + apply H1. apply CRle_refl. +Qed. + +Add Parametric Morphism {R : ConstructiveReals} : (CRabs R) + with signature CReq R ==> CReq R + as CRabs_morph_prop. +Proof. + intros. apply CRabs_morph, H. +Qed. + +Lemma CRabs_right : forall {R : ConstructiveReals} (x : CRcarrier R), + 0 <= x -> CRabs R x == x. +Proof. + intros. split. + - pose proof (CRabs_def R x (CRabs R x)) as [_ H1]. + apply H1, CRle_refl. + - rewrite <- CRabs_def. split. apply CRle_refl. + apply (CRle_trans _ (CRzero R)). 2: exact H. + apply (CRle_trans _ (CRopp R (CRzero R))). + intro abs. apply CRopp_lt_cancel in abs. contradiction. + apply (CRplus_le_reg_l (CRzero R)). + apply (CRle_trans _ (CRzero R)). apply CRplus_opp_r. + apply CRplus_0_r. +Qed. + +Lemma CRabs_opp : forall {R : ConstructiveReals} (x : CRcarrier R), + CRabs R (- x) == CRabs R x. +Proof. + intros. split. + - rewrite <- CRabs_def. split. + + pose proof (CRabs_def R (CRopp R x) (CRabs R (CRopp R x))) as [_ H1]. + specialize (H1 (CRle_refl (CRabs R (CRopp R x)))) as [_ H1]. + apply (CRle_trans _ (CRopp R (CRopp R x))). + 2: exact H1. apply (CRopp_involutive x). + + pose proof (CRabs_def R (CRopp R x) (CRabs R (CRopp R x))) as [_ H1]. + apply H1, CRle_refl. + - rewrite <- CRabs_def. split. + + pose proof (CRabs_def R x (CRabs R x)) as [_ H1]. + apply H1, CRle_refl. + + apply (CRle_trans _ x). apply CRopp_involutive. + pose proof (CRabs_def R x (CRabs R x)) as [_ H1]. + apply H1, CRle_refl. +Qed. + +Lemma CRabs_minus_sym : forall {R : ConstructiveReals} (x y : CRcarrier R), + CRabs R (x - y) == CRabs R (y - x). +Proof. + intros R x y. setoid_replace (x - y) with (-(y-x)). + rewrite CRabs_opp. reflexivity. unfold CRminus. + rewrite CRopp_plus_distr, CRplus_comm, CRopp_involutive. + reflexivity. +Qed. + +Lemma CRabs_left : forall {R : ConstructiveReals} (x : CRcarrier R), + x <= 0 -> CRabs R x == - x. +Proof. + intros. rewrite <- CRabs_opp. apply CRabs_right. + rewrite <- CRopp_0. apply CRopp_ge_le_contravar, H. +Qed. + +Lemma CRabs_triang : forall {R : ConstructiveReals} (x y : CRcarrier R), + CRabs R (x + y) <= CRabs R x + CRabs R y. +Proof. + intros. rewrite <- CRabs_def. split. + - apply (CRle_trans _ (CRplus R (CRabs R x) y)). + apply CRplus_le_compat_r. + pose proof (CRabs_def R x (CRabs R x)) as [_ H1]. + apply H1, CRle_refl. + apply CRplus_le_compat_l. + pose proof (CRabs_def R y (CRabs R y)) as [_ H1]. + apply H1, CRle_refl. + - apply (CRle_trans _ (CRplus R (CRopp R x) (CRopp R y))). + apply CRopp_plus_distr. + apply (CRle_trans _ (CRplus R (CRabs R x) (CRopp R y))). + apply CRplus_le_compat_r. + pose proof (CRabs_def R x (CRabs R x)) as [_ H1]. + apply H1, CRle_refl. + apply CRplus_le_compat_l. + pose proof (CRabs_def R y (CRabs R y)) as [_ H1]. + apply H1, CRle_refl. +Qed. + +Lemma CRabs_le : forall {R : ConstructiveReals} (a b:CRcarrier R), + (-b <= a /\ a <= b) -> CRabs R a <= b. +Proof. + intros. pose proof (CRabs_def R a b) as [H0 _]. + apply H0. split. apply H. destruct H. + rewrite <- (CRopp_involutive b). + apply CRopp_ge_le_contravar. exact H. +Qed. + +Lemma CRabs_triang_inv : forall {R : ConstructiveReals} (x y : CRcarrier R), + CRabs R x - CRabs R y <= CRabs R (x - y). +Proof. + intros. apply (CRplus_le_reg_r (CRabs R y)). + unfold CRminus. rewrite CRplus_assoc, CRplus_opp_l. + rewrite CRplus_0_r. + apply (CRle_trans _ (CRabs R (x - y + y))). + setoid_replace (x - y + y) with x. apply CRle_refl. + unfold CRminus. rewrite CRplus_assoc, CRplus_opp_l. + rewrite CRplus_0_r. reflexivity. + apply CRabs_triang. +Qed. + +Lemma CRabs_triang_inv2 : forall {R : ConstructiveReals} (x y : CRcarrier R), + CRabs R (CRabs R x - CRabs R y) <= CRabs R (x - y). +Proof. + intros. apply CRabs_le. split. + 2: apply CRabs_triang_inv. + apply (CRplus_le_reg_r (CRabs R y)). + unfold CRminus. rewrite CRplus_assoc, CRplus_opp_l. + rewrite CRplus_0_r. fold (x - y). + rewrite CRplus_comm, CRabs_minus_sym. + apply (CRle_trans _ _ _ (CRabs_triang_inv y (y-x))). + setoid_replace (y - (y - x)) with x. apply CRle_refl. + unfold CRminus. rewrite CRopp_plus_distr, <- CRplus_assoc. + rewrite CRplus_opp_r, CRplus_0_l. apply CRopp_involutive. +Qed. + +Lemma CR_of_Q_abs : forall {R : ConstructiveReals} (q : Q), + CRabs R (CR_of_Q R q) == CR_of_Q R (Qabs q). +Proof. + intros. destruct (Qlt_le_dec 0 q). + - apply (CReq_trans _ (CR_of_Q R q)). + apply CRabs_right. apply (CRle_trans _ (CR_of_Q R 0)). + apply CR_of_Q_zero. apply CR_of_Q_le. apply Qlt_le_weak, q0. + apply CR_of_Q_morph. symmetry. apply Qabs_pos, Qlt_le_weak, q0. + - apply (CReq_trans _ (CR_of_Q R (-q))). + apply (CReq_trans _ (CRabs R (CRopp R (CR_of_Q R q)))). + apply CReq_sym, CRabs_opp. + 2: apply CR_of_Q_morph; symmetry; apply Qabs_neg, q0. + apply (CReq_trans _ (CRopp R (CR_of_Q R q))). + 2: apply CReq_sym, CR_of_Q_opp. + apply CRabs_right. apply (CRle_trans _ (CR_of_Q R 0)). + apply CR_of_Q_zero. + apply (CRle_trans _ (CR_of_Q R (-q))). apply CR_of_Q_le. + apply (Qplus_le_l _ _ q). ring_simplify. exact q0. + apply CR_of_Q_opp. +Qed. + +Lemma CRle_abs : forall {R : ConstructiveReals} (x : CRcarrier R), + x <= CRabs R x. +Proof. + intros. pose proof (CRabs_def R x (CRabs R x)) as [_ H]. + apply H, CRle_refl. +Qed. + +Lemma CRabs_pos : forall {R : ConstructiveReals} (x : CRcarrier R), + 0 <= CRabs R x. +Proof. + intros. intro abs. destruct (CRltLinear R). clear p. + specialize (s _ x _ abs). destruct s. + exact (CRle_abs x c). rewrite CRabs_left in abs. + rewrite <- CRopp_0 in abs. apply CRopp_lt_cancel in abs. + exact (CRlt_asym _ _ abs c). apply CRlt_asym, c. +Qed. + +Lemma CRabs_appart_0 : forall {R : ConstructiveReals} (x : CRcarrier R), + 0 < CRabs R x -> x ≶ 0. +Proof. + intros. destruct (CRltLinear R). clear p. + pose proof (s _ x _ H) as [pos|neg]. + right. exact pos. left. + destruct (CR_Q_dense R _ _ neg) as [q [H0 H1]]. + destruct (Qlt_le_dec 0 q). + - destruct (s (CR_of_Q R (-q)) x 0). + rewrite <- CR_of_Q_zero. apply CR_of_Q_lt. + apply (Qplus_lt_l _ _ q). ring_simplify. exact q0. + exfalso. pose proof (CRabs_def R x (CR_of_Q R q)) as [H2 _]. + apply H2. clear H2. split. apply CRlt_asym, H0. + 2: exact H1. rewrite <- Qopp_involutive, CR_of_Q_opp. + apply CRopp_ge_le_contravar, CRlt_asym, c. exact c. + - apply (CRlt_le_trans _ _ _ H0). + rewrite <- CR_of_Q_zero. apply CR_of_Q_le. exact q0. +Qed. + + +(* The proof by cases on the signs of x and y applies constructively, + because of the positivity hypotheses. *) +Lemma CRabs_mult : forall {R : ConstructiveReals} (x y : CRcarrier R), + CRabs R (x * y) == CRabs R x * CRabs R y. +Proof. + intro R. + assert (forall (x y : CRcarrier R), + x ≶ 0 + -> y ≶ 0 + -> CRabs R (x * y) == CRabs R x * CRabs R y) as prep. + { intros. destruct H, H0. + + rewrite CRabs_right, CRabs_left, CRabs_left. + rewrite <- CRopp_mult_distr_l, CRopp_mult_distr_r, CRopp_involutive. + reflexivity. + apply CRlt_asym, c0. apply CRlt_asym, c. + setoid_replace (x*y) with (- x * - y). + apply CRlt_asym, CRmult_lt_0_compat. + rewrite <- CRopp_0. apply CRopp_gt_lt_contravar, c. + rewrite <- CRopp_0. apply CRopp_gt_lt_contravar, c0. + rewrite <- CRopp_mult_distr_l, CRopp_mult_distr_r, CRopp_involutive. + reflexivity. + + rewrite CRabs_left, CRabs_left, CRabs_right. + rewrite <- CRopp_mult_distr_l. reflexivity. + apply CRlt_asym, c0. apply CRlt_asym, c. + rewrite <- (CRmult_0_l y). + apply CRmult_le_compat_r_half. exact c0. + apply CRlt_asym, c. + + rewrite CRabs_left, CRabs_right, CRabs_left. + rewrite <- CRopp_mult_distr_r. reflexivity. + apply CRlt_asym, c0. apply CRlt_asym, c. + rewrite <- (CRmult_0_r x). + apply CRmult_le_compat_l_half. + exact c. apply CRlt_asym, c0. + + rewrite CRabs_right, CRabs_right, CRabs_right. reflexivity. + apply CRlt_asym, c0. apply CRlt_asym, c. + apply CRlt_asym, CRmult_lt_0_compat; assumption. } + split. + - intro abs. + assert (0 < CRabs R x * CRabs R y). + { apply (CRle_lt_trans _ (CRabs R (x*y))). + apply CRabs_pos. exact abs. } + pose proof (CRmult_pos_appart_zero _ _ H). + rewrite CRmult_comm in H. + apply CRmult_pos_appart_zero in H. + destruct H. 2: apply (CRabs_pos y c). + destruct H0. 2: apply (CRabs_pos x c0). + apply CRabs_appart_0 in c. + apply CRabs_appart_0 in c0. + rewrite (prep x y) in abs. + exact (CRlt_asym _ _ abs abs). exact c0. exact c. + - intro abs. + assert (0 < CRabs R (x * y)). + { apply (CRle_lt_trans _ (CRabs R x * CRabs R y)). + rewrite <- (CRmult_0_l (CRabs R y)). + apply CRmult_le_compat_r. + apply CRabs_pos. apply CRabs_pos. exact abs. } + apply CRabs_appart_0 in H. destruct H. + + apply CRopp_gt_lt_contravar in c. + rewrite CRopp_0, CRopp_mult_distr_l in c. + pose proof (CRmult_pos_appart_zero _ _ c). + rewrite CRmult_comm in c. + apply CRmult_pos_appart_zero in c. + rewrite (prep x y) in abs. + exact (CRlt_asym _ _ abs abs). + destruct H. left. apply CRopp_gt_lt_contravar in c0. + rewrite CRopp_involutive, CRopp_0 in c0. exact c0. + right. apply CRopp_gt_lt_contravar in c0. + rewrite CRopp_involutive, CRopp_0 in c0. exact c0. + destruct c. right. exact c. left. exact c. + + pose proof (CRmult_pos_appart_zero _ _ c). + rewrite CRmult_comm in c. + apply CRmult_pos_appart_zero in c. + rewrite (prep x y) in abs. + exact (CRlt_asym _ _ abs abs). + destruct H. right. exact c0. left. exact c0. + destruct c. right. exact c. left. exact c. +Qed. + +Lemma CRabs_lt : forall {R : ConstructiveReals} (x y : CRcarrier R), + CRabs _ x < y -> prod (x < y) (-x < y). +Proof. + split. + - apply (CRle_lt_trans _ _ _ (CRle_abs x)), H. + - apply (CRle_lt_trans _ _ _ (CRle_abs (-x))). + rewrite CRabs_opp. exact H. +Qed. + +Lemma CRabs_def1 : forall {R : ConstructiveReals} (x y : CRcarrier R), + x < y -> -x < y -> CRabs _ x < y. +Proof. + intros. destruct (CRltLinear R), p. + destruct (s x (CRabs R x) y H). 2: exact c0. + rewrite CRabs_left. exact H0. intro abs. + rewrite CRabs_right in c0. exact (CRlt_asym x x c0 c0). + apply CRlt_asym, abs. +Qed. + +Lemma CRabs_def2 : forall {R : ConstructiveReals} (x a:CRcarrier R), + CRabs _ x <= a -> (x <= a) /\ (- a <= x). +Proof. + split. + - exact (CRle_trans _ _ _ (CRle_abs _) H). + - rewrite <- (CRopp_involutive x). + apply CRopp_ge_le_contravar. + rewrite <- CRabs_opp in H. + exact (CRle_trans _ _ _ (CRle_abs _) H). +Qed. + + +(* Minimum *) + +Definition CRmin {R : ConstructiveReals} (x y : CRcarrier R) : CRcarrier R + := (x + y - CRabs _ (y - x)) * CR_of_Q _ (1#2). + +Lemma CRmin_lt_r : forall {R : ConstructiveReals} (x y : CRcarrier R), + CRmin x y < y -> CRmin x y == x. +Proof. + intros. unfold CRmin. unfold CRmin in H. + apply (CRmult_eq_reg_r (CR_of_Q R 2)). + left; apply CR_of_Q_pos; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + rewrite (CR_of_Q_plus R 1 1), CR_of_Q_one, CRmult_plus_distr_l, CRmult_1_r. + rewrite CRabs_right. unfold CRminus. + rewrite CRopp_plus_distr, CRplus_assoc, <- (CRplus_assoc y). + rewrite CRplus_opp_r, CRplus_0_l, CRopp_involutive. reflexivity. + apply (CRmult_lt_compat_r (CR_of_Q R 2)) in H. + 2: apply CR_of_Q_pos; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult in H. + setoid_replace ((1 # 2) * 2)%Q with 1%Q in H. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r in H. + rewrite CRmult_comm, (CR_of_Q_plus R 1 1), CR_of_Q_one, CRmult_plus_distr_r, + CRmult_1_l in H. + intro abs. rewrite CRabs_left in H. + unfold CRminus in H. + rewrite CRopp_involutive, CRplus_comm in H. + rewrite CRplus_assoc, <- (CRplus_assoc (-x)), CRplus_opp_l in H. + rewrite CRplus_0_l in H. exact (CRlt_asym _ _ H H). + apply CRlt_asym, abs. +Qed. + +Add Parametric Morphism {R : ConstructiveReals} : CRmin + with signature (CReq R) ==> (CReq R) ==> (CReq R) + as CRmin_morph. +Proof. + intros. unfold CRmin. + apply CRmult_morph. 2: reflexivity. + unfold CRminus. + rewrite H, H0. reflexivity. +Qed. + +Instance CRmin_morphT + : forall {R : ConstructiveReals}, + CMorphisms.Proper + (CMorphisms.respectful (CReq R) (CMorphisms.respectful (CReq R) (CReq R))) (@CRmin R). +Proof. + intros R x y H z t H0. + rewrite H, H0. reflexivity. +Qed. + +Lemma CRmin_l : forall {R : ConstructiveReals} (x y : CRcarrier R), + CRmin x y <= x. +Proof. + intros. unfold CRmin. + apply (CRmult_le_reg_r (CR_of_Q R 2)). + rewrite <- CR_of_Q_zero. apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + rewrite (CR_of_Q_plus _ 1 1), CRmult_plus_distr_l, CR_of_Q_one, CRmult_1_r. + unfold CRminus. rewrite CRplus_assoc. apply CRplus_le_compat_l. + apply (CRplus_le_reg_r (CRabs _ (y + - x)+ -x)). + rewrite CRplus_assoc, <- (CRplus_assoc (-CRabs _ (y + - x))). + rewrite CRplus_opp_l, CRplus_0_l. + rewrite (CRplus_comm x), CRplus_assoc, CRplus_opp_l, CRplus_0_r. + apply CRle_abs. +Qed. + +Lemma CRmin_r : forall {R : ConstructiveReals} (x y : CRcarrier R), + CRmin x y <= y. +Proof. + intros. unfold CRmin. + apply (CRmult_le_reg_r (CR_of_Q R 2)). + rewrite <- CR_of_Q_zero. apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + rewrite (CR_of_Q_plus _ 1 1), CRmult_plus_distr_l, CR_of_Q_one, CRmult_1_r. + rewrite (CRplus_comm x). + unfold CRminus. rewrite CRplus_assoc. apply CRplus_le_compat_l. + apply (CRplus_le_reg_l (-x)). + rewrite <- CRplus_assoc, CRplus_opp_l, CRplus_0_l. + rewrite <- (CRopp_involutive y), <- CRopp_plus_distr, <- CRopp_plus_distr. + apply CRopp_ge_le_contravar. rewrite CRabs_opp, CRplus_comm. + apply CRle_abs. +Qed. + +Lemma CRnegPartAbsMin : forall {R : ConstructiveReals} (x : CRcarrier R), + CRmin 0 x == (x - CRabs _ x) * (CR_of_Q _ (1#2)). +Proof. + intros. unfold CRmin. unfold CRminus. rewrite CRplus_0_l. + apply CRmult_morph. 2: reflexivity. rewrite CRopp_0, CRplus_0_r. reflexivity. +Qed. + +Lemma CRmin_sym : forall {R : ConstructiveReals} (x y : CRcarrier R), + CRmin x y == CRmin y x. +Proof. + intros. unfold CRmin. apply CRmult_morph. 2: reflexivity. + rewrite CRabs_minus_sym. unfold CRminus. + rewrite (CRplus_comm x y). reflexivity. +Qed. + +Lemma CRmin_mult : + forall {R : ConstructiveReals} (p q r : CRcarrier R), + 0 <= r -> CRmin (r * p) (r * q) == r * CRmin p q. +Proof. + intros R p q r H. unfold CRmin. + setoid_replace (r * q - r * p) with (r * (q - p)). + rewrite CRabs_mult. + rewrite (CRabs_right r). 2: exact H. + rewrite <- CRmult_assoc. apply CRmult_morph. 2: reflexivity. + unfold CRminus. rewrite CRopp_mult_distr_r. + do 2 rewrite <- CRmult_plus_distr_l. reflexivity. + unfold CRminus. rewrite CRopp_mult_distr_r. + rewrite <- CRmult_plus_distr_l. reflexivity. +Qed. + +Lemma CRmin_plus : forall {R : ConstructiveReals} (x y z : CRcarrier R), + x + CRmin y z == CRmin (x + y) (x + z). +Proof. + intros. unfold CRmin. + unfold CRminus. setoid_replace (x + z + - (x + y)) with (z-y). + apply (CRmult_eq_reg_r (CR_of_Q _ 2)). + left. rewrite <- CR_of_Q_zero. apply CR_of_Q_lt; reflexivity. + rewrite CRmult_plus_distr_r. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + rewrite (CR_of_Q_plus _ 1 1), CRmult_plus_distr_l, CR_of_Q_one, CRmult_1_r. + do 3 rewrite (CRplus_assoc x). apply CRplus_morph. reflexivity. + do 2 rewrite <- CRplus_assoc. apply CRplus_morph. 2: reflexivity. + rewrite (CRplus_comm x). apply CRplus_assoc. + rewrite CRopp_plus_distr. rewrite <- CRplus_assoc. + apply CRplus_morph. 2: reflexivity. + rewrite CRplus_comm, <- CRplus_assoc, CRplus_opp_l. + apply CRplus_0_l. +Qed. + +Lemma CRmin_left : forall {R : ConstructiveReals} (x y : CRcarrier R), + x <= y -> CRmin x y == x. +Proof. + intros. unfold CRmin. + apply (CRmult_eq_reg_r (CR_of_Q R 2)). + left. rewrite <- CR_of_Q_zero. apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + rewrite (CR_of_Q_plus _ 1 1), CRmult_plus_distr_l, CR_of_Q_one, CRmult_1_r. + rewrite CRabs_right. unfold CRminus. rewrite CRopp_plus_distr. + rewrite CRplus_assoc. apply CRplus_morph. reflexivity. + rewrite <- CRplus_assoc, CRplus_opp_r, CRplus_0_l. apply CRopp_involutive. + rewrite <- (CRplus_opp_r x). apply CRplus_le_compat. + exact H. apply CRle_refl. +Qed. + +Lemma CRmin_right : forall {R : ConstructiveReals} (x y : CRcarrier R), + y <= x -> CRmin x y == y. +Proof. + intros. unfold CRmin. + apply (CRmult_eq_reg_r (CR_of_Q R 2)). + left. rewrite <- CR_of_Q_zero. apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + rewrite (CR_of_Q_plus _ 1 1), CRmult_plus_distr_l, CR_of_Q_one, CRmult_1_r. + rewrite CRabs_left. unfold CRminus. do 2 rewrite CRopp_plus_distr. + rewrite (CRplus_comm x y). + rewrite CRplus_assoc. apply CRplus_morph. reflexivity. + do 2 rewrite CRopp_involutive. + rewrite CRplus_comm, CRplus_assoc, CRplus_opp_l, CRplus_0_r. reflexivity. + rewrite <- (CRplus_opp_r x). apply CRplus_le_compat. + exact H. apply CRle_refl. +Qed. + +Lemma CRmin_lt : forall {R : ConstructiveReals} (x y z : CRcarrier R), + z < x -> z < y -> z < CRmin x y. +Proof. + intros. unfold CRmin. + apply (CRmult_lt_reg_r (CR_of_Q R 2)). + rewrite <- CR_of_Q_zero. apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + apply (CRplus_lt_reg_l _ (CRabs _ (y - x) - (z*CR_of_Q R 2))). + unfold CRminus. rewrite CRplus_assoc. rewrite CRplus_opp_l, CRplus_0_r. + rewrite (CRplus_comm (CRabs R (y + - x))). + rewrite (CRplus_comm (x+y)), CRplus_assoc. + rewrite <- (CRplus_assoc (CRabs R (y + - x))), CRplus_opp_r, CRplus_0_l. + rewrite <- (CRplus_comm (x+y)). + apply CRabs_def1. + - unfold CRminus. rewrite <- (CRplus_comm y), CRplus_assoc. + apply CRplus_lt_compat_l. + apply (CRplus_lt_reg_l R (-x)). + rewrite CRopp_mult_distr_l. + rewrite <- CRplus_assoc, CRplus_opp_l, CRplus_0_l. + rewrite (CR_of_Q_plus R 1 1), CR_of_Q_one, CRmult_plus_distr_l. + rewrite CRmult_1_r. apply CRplus_le_lt_compat. + apply CRlt_asym. + apply CRopp_gt_lt_contravar, H. + apply CRopp_gt_lt_contravar, H. + - rewrite CRopp_plus_distr, CRopp_involutive. + rewrite CRplus_comm, CRplus_assoc. + apply CRplus_lt_compat_l. + apply (CRplus_lt_reg_l R (-y)). + rewrite CRopp_mult_distr_l. + rewrite <- CRplus_assoc, CRplus_opp_l, CRplus_0_l. + rewrite (CR_of_Q_plus R 1 1), CR_of_Q_one, CRmult_plus_distr_l. + rewrite CRmult_1_r. apply CRplus_le_lt_compat. + apply CRlt_asym. + apply CRopp_gt_lt_contravar, H0. + apply CRopp_gt_lt_contravar, H0. +Qed. + +Lemma CRmin_contract : forall {R : ConstructiveReals} (x y a : CRcarrier R), + CRabs _ (CRmin x a - CRmin y a) <= CRabs _ (x - y). +Proof. + intros. unfold CRmin. + unfold CRminus. rewrite CRopp_mult_distr_l, <- CRmult_plus_distr_r. + rewrite (CRabs_morph + _ ((x - y + (CRabs _ (a - y) - CRabs _ (a - x))) * CR_of_Q R (1 # 2))). + rewrite CRabs_mult, (CRabs_right (CR_of_Q R (1 # 2))). + 2: rewrite <- CR_of_Q_zero; apply CR_of_Q_le; discriminate. + apply (CRle_trans _ + ((CRabs _ (x - y) * 1 + CRabs _ (x-y) * 1) + * CR_of_Q R (1 # 2))). + apply CRmult_le_compat_r. + rewrite <- CR_of_Q_zero. apply CR_of_Q_le. discriminate. + apply (CRle_trans + _ (CRabs _ (x - y) + CRabs _ (CRabs _ (a - y) - CRabs _ (a - x)))). + apply CRabs_triang. rewrite CRmult_1_r. apply CRplus_le_compat_l. + rewrite (CRabs_morph (x-y) ((a-y)-(a-x))). + apply CRabs_triang_inv2. + unfold CRminus. rewrite (CRplus_comm (a + - y)). + rewrite <- CRplus_assoc. apply CRplus_morph. 2: reflexivity. + rewrite CRplus_comm, CRopp_plus_distr, <- CRplus_assoc. + rewrite CRplus_opp_r, CRopp_involutive, CRplus_0_l. + reflexivity. + rewrite <- CRmult_plus_distr_l, <- CR_of_Q_one. + rewrite <- (CR_of_Q_plus R 1 1). + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 + 1) * (1 # 2))%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. apply CRle_refl. + unfold CRminus. apply CRmult_morph. 2: reflexivity. + do 4 rewrite CRplus_assoc. apply CRplus_morph. reflexivity. + rewrite <- CRplus_assoc. rewrite CRplus_comm, CRopp_plus_distr. + rewrite CRplus_assoc. apply CRplus_morph. reflexivity. + rewrite CRopp_plus_distr. rewrite (CRplus_comm (-a)). + rewrite CRplus_assoc, <- (CRplus_assoc (-a)), CRplus_opp_l. + rewrite CRplus_0_l, CRopp_involutive. reflexivity. +Qed. + +Lemma CRmin_glb : forall {R : ConstructiveReals} (x y z:CRcarrier R), + z <= x -> z <= y -> z <= CRmin x y. +Proof. + intros. unfold CRmin. + apply (CRmult_le_reg_r (CR_of_Q R 2)). + rewrite <- CR_of_Q_zero. apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + apply (CRplus_le_reg_l (CRabs _ (y-x) - (z*CR_of_Q R 2))). + unfold CRminus. rewrite CRplus_assoc, CRplus_opp_l, CRplus_0_r. + rewrite (CRplus_comm (CRabs R (y + - x) + - (z * CR_of_Q R 2))). + rewrite CRplus_assoc, <- (CRplus_assoc (- CRabs R (y + - x))). + rewrite CRplus_opp_l, CRplus_0_l. + apply CRabs_le. split. + - do 2 rewrite CRopp_plus_distr. + rewrite CRopp_involutive, (CRplus_comm y), CRplus_assoc. + apply CRplus_le_compat_l, (CRplus_le_reg_l y). + rewrite <- CRplus_assoc, CRplus_opp_r, CRplus_0_l. + rewrite (CR_of_Q_plus R 1 1), CR_of_Q_one, CRmult_plus_distr_l. + rewrite CRmult_1_r. apply CRplus_le_compat; exact H0. + - rewrite (CRplus_comm x), CRplus_assoc. apply CRplus_le_compat_l. + apply (CRplus_le_reg_l (-x)). + rewrite <- CRplus_assoc, CRplus_opp_l, CRplus_0_l. + rewrite CRopp_mult_distr_l. + rewrite (CR_of_Q_plus R 1 1), CR_of_Q_one, CRmult_plus_distr_l. + rewrite CRmult_1_r. + apply CRplus_le_compat; apply CRopp_ge_le_contravar; exact H. +Qed. + +Lemma CRmin_assoc : forall {R : ConstructiveReals} (a b c : CRcarrier R), + CRmin a (CRmin b c) == CRmin (CRmin a b) c. +Proof. + split. + - apply CRmin_glb. + + apply (CRle_trans _ (CRmin a b)). + apply CRmin_l. apply CRmin_l. + + apply CRmin_glb. + apply (CRle_trans _ (CRmin a b)). + apply CRmin_l. apply CRmin_r. apply CRmin_r. + - apply CRmin_glb. + + apply CRmin_glb. apply CRmin_l. + apply (CRle_trans _ (CRmin b c)). + apply CRmin_r. apply CRmin_l. + + apply (CRle_trans _ (CRmin b c)). + apply CRmin_r. apply CRmin_r. +Qed. + +Lemma CRlt_min : forall {R : ConstructiveReals} (x y z : CRcarrier R), + z < CRmin x y -> prod (z < x) (z < y). +Proof. + intros. destruct (CR_Q_dense R _ _ H) as [q qmaj]. + destruct qmaj. + split. + - apply (CRlt_le_trans _ (CR_of_Q R q) _ c). + intro abs. apply (CRlt_asym _ _ c0). + apply (CRle_lt_trans _ x). apply CRmin_l. exact abs. + - apply (CRlt_le_trans _ (CR_of_Q R q) _ c). + intro abs. apply (CRlt_asym _ _ c0). + apply (CRle_lt_trans _ y). apply CRmin_r. exact abs. +Qed. + + + +(* Maximum *) + +Definition CRmax {R : ConstructiveReals} (x y : CRcarrier R) : CRcarrier R + := (x + y + CRabs _ (y - x)) * CR_of_Q _ (1#2). + +Add Parametric Morphism {R : ConstructiveReals} : CRmax + with signature (CReq R) ==> (CReq R) ==> (CReq R) + as CRmax_morph. +Proof. + intros. unfold CRmax. + apply CRmult_morph. 2: reflexivity. unfold CRminus. + rewrite H, H0. reflexivity. +Qed. + +Instance CRmax_morphT + : forall {R : ConstructiveReals}, + CMorphisms.Proper + (CMorphisms.respectful (CReq R) (CMorphisms.respectful (CReq R) (CReq R))) (@CRmax R). +Proof. + intros R x y H z t H0. + rewrite H, H0. reflexivity. +Qed. + +Lemma CRmax_lub : forall {R : ConstructiveReals} (x y z:CRcarrier R), + x <= z -> y <= z -> CRmax x y <= z. +Proof. + intros. unfold CRmax. + apply (CRmult_le_reg_r (CR_of_Q _ 2)). rewrite <- CR_of_Q_zero. + apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + apply (CRplus_le_reg_l (-x-y)). + rewrite <- CRplus_assoc. unfold CRminus. + rewrite <- CRopp_plus_distr, CRplus_opp_l, CRplus_0_l. + apply CRabs_le. split. + - repeat rewrite CRopp_plus_distr. + do 2 rewrite CRopp_involutive. + rewrite (CRplus_comm x), CRplus_assoc. apply CRplus_le_compat_l. + apply (CRplus_le_reg_l (-x)). + rewrite <- CRplus_assoc, CRplus_opp_l, CRplus_0_l. + rewrite (CR_of_Q_plus _ 1 1), CRmult_plus_distr_l, CR_of_Q_one, CRmult_1_r. + rewrite CRopp_plus_distr. + apply CRplus_le_compat; apply CRopp_ge_le_contravar; assumption. + - rewrite (CRplus_comm y), CRopp_plus_distr, CRplus_assoc. + apply CRplus_le_compat_l. + apply (CRplus_le_reg_l y). + rewrite <- CRplus_assoc, CRplus_opp_r, CRplus_0_l. + rewrite (CR_of_Q_plus _ 1 1), CRmult_plus_distr_l, CR_of_Q_one, CRmult_1_r. + apply CRplus_le_compat; assumption. +Qed. + +Lemma CRmax_l : forall {R : ConstructiveReals} (x y : CRcarrier R), + x <= CRmax x y. +Proof. + intros. unfold CRmax. + apply (CRmult_le_reg_r (CR_of_Q R 2)). rewrite <- CR_of_Q_zero. + apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + setoid_replace 2%Q with (1+1)%Q. rewrite CR_of_Q_plus, CR_of_Q_one. + rewrite CRmult_plus_distr_l, CRmult_1_r, CRplus_assoc. + apply CRplus_le_compat_l. + apply (CRplus_le_reg_l (-y)). + rewrite <- CRplus_assoc, CRplus_opp_l, CRplus_0_l. + rewrite CRabs_minus_sym, CRplus_comm. + apply CRle_abs. reflexivity. +Qed. + +Lemma CRmax_r : forall {R : ConstructiveReals} (x y : CRcarrier R), + y <= CRmax x y. +Proof. + intros. unfold CRmax. + apply (CRmult_le_reg_r (CR_of_Q _ 2)). rewrite <- CR_of_Q_zero. + apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + rewrite (CR_of_Q_plus _ 1 1), CRmult_plus_distr_l, CR_of_Q_one, CRmult_1_r. + rewrite (CRplus_comm x). + rewrite CRplus_assoc. apply CRplus_le_compat_l. + apply (CRplus_le_reg_l (-x)). + rewrite <- CRplus_assoc, CRplus_opp_l, CRplus_0_l. + rewrite CRplus_comm. apply CRle_abs. +Qed. + +Lemma CRposPartAbsMax : forall {R : ConstructiveReals} (x : CRcarrier R), + CRmax 0 x == (x + CRabs _ x) * (CR_of_Q R (1#2)). +Proof. + intros. unfold CRmax. unfold CRminus. rewrite CRplus_0_l. + apply CRmult_morph. 2: reflexivity. rewrite CRopp_0, CRplus_0_r. reflexivity. +Qed. + +Lemma CRmax_sym : forall {R : ConstructiveReals} (x y : CRcarrier R), + CRmax x y == CRmax y x. +Proof. + intros. unfold CRmax. + rewrite CRabs_minus_sym. apply CRmult_morph. + 2: reflexivity. rewrite (CRplus_comm x y). reflexivity. +Qed. + +Lemma CRmax_plus : forall {R : ConstructiveReals} (x y z : CRcarrier R), + x + CRmax y z == CRmax (x + y) (x + z). +Proof. + intros. unfold CRmax. + setoid_replace (x + z - (x + y)) with (z-y). + apply (CRmult_eq_reg_r (CR_of_Q _ 2)). + left. rewrite <- CR_of_Q_zero. apply CR_of_Q_lt; reflexivity. + rewrite CRmult_plus_distr_r. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite (CR_of_Q_plus _ 1 1), CRmult_plus_distr_l, CR_of_Q_one, CRmult_1_r. + rewrite CRmult_1_r. + do 3 rewrite (CRplus_assoc x). apply CRplus_morph. reflexivity. + do 2 rewrite <- CRplus_assoc. apply CRplus_morph. 2: reflexivity. + rewrite (CRplus_comm x). apply CRplus_assoc. + unfold CRminus. rewrite CRopp_plus_distr. rewrite <- CRplus_assoc. + apply CRplus_morph. 2: reflexivity. + rewrite CRplus_comm, <- CRplus_assoc, CRplus_opp_l. + apply CRplus_0_l. +Qed. + +Lemma CRmax_left : forall {R : ConstructiveReals} (x y : CRcarrier R), + y <= x -> CRmax x y == x. +Proof. + intros. unfold CRmax. + apply (CRmult_eq_reg_r (CR_of_Q R 2)). + left. rewrite <- CR_of_Q_zero. apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + rewrite (CR_of_Q_plus _ 1 1), CRmult_plus_distr_l, CR_of_Q_one, CRmult_1_r. + rewrite CRplus_assoc. apply CRplus_morph. reflexivity. + rewrite CRabs_left. unfold CRminus. rewrite CRopp_plus_distr, CRopp_involutive. + rewrite <- CRplus_assoc, CRplus_opp_r, CRplus_0_l. reflexivity. + rewrite <- (CRplus_opp_r x). apply CRplus_le_compat_r. exact H. +Qed. + +Lemma CRmax_right : forall {R : ConstructiveReals} (x y : CRcarrier R), + x <= y -> CRmax x y == y. +Proof. + intros. unfold CRmax. + apply (CRmult_eq_reg_r (CR_of_Q R 2)). + left. rewrite <- CR_of_Q_zero. apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + rewrite (CR_of_Q_plus _ 1 1), CRmult_plus_distr_l, CR_of_Q_one, CRmult_1_r. + rewrite (CRplus_comm x y). + rewrite CRplus_assoc. apply CRplus_morph. reflexivity. + rewrite CRabs_right. unfold CRminus. rewrite CRplus_comm. + rewrite CRplus_assoc, CRplus_opp_l, CRplus_0_r. reflexivity. + rewrite <- (CRplus_opp_r x). apply CRplus_le_compat_r. exact H. +Qed. + +Lemma CRmax_contract : forall {R : ConstructiveReals} (x y a : CRcarrier R), + CRabs _ (CRmax x a - CRmax y a) <= CRabs _ (x - y). +Proof. + intros. unfold CRmax. + rewrite (CRabs_morph + _ ((x - y + (CRabs _ (a - x) - CRabs _ (a - y))) * CR_of_Q R (1 # 2))). + rewrite CRabs_mult, (CRabs_right (CR_of_Q R (1 # 2))). + 2: rewrite <- CR_of_Q_zero; apply CR_of_Q_le; discriminate. + apply (CRle_trans + _ ((CRabs _ (x - y) * 1 + CRabs _ (x-y) * 1) + * CR_of_Q R (1 # 2))). + apply CRmult_le_compat_r. + rewrite <- CR_of_Q_zero. apply CR_of_Q_le. discriminate. + apply (CRle_trans + _ (CRabs _ (x - y) + CRabs _ (CRabs _ (a - x) - CRabs _ (a - y)))). + apply CRabs_triang. rewrite CRmult_1_r. apply CRplus_le_compat_l. + rewrite (CRabs_minus_sym x y). + rewrite (CRabs_morph (y-x) ((a-x)-(a-y))). + apply CRabs_triang_inv2. + unfold CRminus. rewrite (CRplus_comm (a + - x)). + rewrite <- CRplus_assoc. apply CRplus_morph. 2: reflexivity. + rewrite CRplus_comm, CRopp_plus_distr, <- CRplus_assoc. + rewrite CRplus_opp_r, CRopp_involutive, CRplus_0_l. + reflexivity. + rewrite <- CRmult_plus_distr_l, <- CR_of_Q_one. + rewrite <- (CR_of_Q_plus R 1 1). + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 + 1) * (1 # 2))%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. apply CRle_refl. + unfold CRminus. rewrite CRopp_mult_distr_l. + rewrite <- CRmult_plus_distr_r. apply CRmult_morph. 2: reflexivity. + do 4 rewrite CRplus_assoc. apply CRplus_morph. reflexivity. + rewrite <- CRplus_assoc. rewrite CRplus_comm, CRopp_plus_distr. + rewrite CRplus_assoc. apply CRplus_morph. reflexivity. + rewrite CRopp_plus_distr. rewrite (CRplus_comm (-a)). + rewrite CRplus_assoc, <- (CRplus_assoc (-a)), CRplus_opp_l. + rewrite CRplus_0_l. apply CRplus_comm. +Qed. + +Lemma CRmax_lub_lt : forall {R : ConstructiveReals} (x y z : CRcarrier R), + x < z -> y < z -> CRmax x y < z. +Proof. + intros. unfold CRmax. + apply (CRmult_lt_reg_r (CR_of_Q R 2)). + rewrite <- CR_of_Q_zero. apply CR_of_Q_lt; reflexivity. + rewrite CRmult_assoc, <- CR_of_Q_mult. + setoid_replace ((1 # 2) * 2)%Q with 1%Q. 2: reflexivity. + rewrite CR_of_Q_one, CRmult_1_r. + apply (CRplus_lt_reg_l _ (-y -x)). unfold CRminus. + rewrite CRplus_assoc, <- (CRplus_assoc (-x)), <- (CRplus_assoc (-x)). + rewrite CRplus_opp_l, CRplus_0_l, <- CRplus_assoc, CRplus_opp_l, CRplus_0_l. + apply CRabs_def1. + - rewrite (CRplus_comm y), (CRplus_comm (-y)), CRplus_assoc. + apply CRplus_lt_compat_l. + apply (CRplus_lt_reg_l _ y). + rewrite <- CRplus_assoc, CRplus_opp_r, CRplus_0_l. + rewrite (CR_of_Q_plus R 1 1), CR_of_Q_one, CRmult_plus_distr_l. + rewrite CRmult_1_r. apply CRplus_le_lt_compat. + apply CRlt_asym, H0. exact H0. + - rewrite CRopp_plus_distr, CRopp_involutive. + rewrite CRplus_assoc. apply CRplus_lt_compat_l. + apply (CRplus_lt_reg_l _ x). + rewrite <- CRplus_assoc, CRplus_opp_r, CRplus_0_l. + rewrite (CR_of_Q_plus R 1 1), CR_of_Q_one, CRmult_plus_distr_l. + rewrite CRmult_1_r. apply CRplus_le_lt_compat. + apply CRlt_asym, H. exact H. +Qed. + +Lemma CRmax_assoc : forall {R : ConstructiveReals} (a b c : CRcarrier R), + CRmax a (CRmax b c) == CRmax (CRmax a b) c. +Proof. + split. + - apply CRmax_lub. + + apply CRmax_lub. apply CRmax_l. + apply (CRle_trans _ (CRmax b c)). + apply CRmax_l. apply CRmax_r. + + apply (CRle_trans _ (CRmax b c)). + apply CRmax_r. apply CRmax_r. + - apply CRmax_lub. + + apply (CRle_trans _ (CRmax a b)). + apply CRmax_l. apply CRmax_l. + + apply CRmax_lub. + apply (CRle_trans _ (CRmax a b)). + apply CRmax_r. apply CRmax_l. apply CRmax_r. +Qed. + +Lemma CRmax_min_mult_neg : + forall {R : ConstructiveReals} (p q r:CRcarrier R), + r <= 0 -> CRmax (r * p) (r * q) == r * CRmin p q. +Proof. + intros R p q r H. unfold CRmin, CRmax. + setoid_replace (r * q - r * p) with (r * (q - p)). + rewrite CRabs_mult. + rewrite (CRabs_left r), <- CRmult_assoc. + apply CRmult_morph. 2: reflexivity. unfold CRminus. + rewrite <- CRopp_mult_distr_l, CRopp_mult_distr_r, + CRmult_plus_distr_l, CRmult_plus_distr_l. + reflexivity. exact H. + unfold CRminus. rewrite CRmult_plus_distr_l, CRopp_mult_distr_r. reflexivity. +Qed. + +Lemma CRlt_max : forall {R : ConstructiveReals} (x y z : CRcarrier R), + CRmax x y < z -> prod (x < z) (y < z). +Proof. + intros. destruct (CR_Q_dense R _ _ H) as [q qmaj]. + destruct qmaj. + split. + - apply (CRlt_le_trans _ (CR_of_Q R q)). + apply (CRle_lt_trans _ (CRmax x y)). apply CRmax_l. exact c. + apply CRlt_asym, c0. + - apply (CRlt_le_trans _ (CR_of_Q R q)). + apply (CRle_lt_trans _ (CRmax x y)). apply CRmax_r. exact c. + apply CRlt_asym, c0. +Qed. + +Lemma CRmax_mult : + forall {R : ConstructiveReals} (p q r:CRcarrier R), + 0 <= r -> CRmax (r * p) (r * q) == r * CRmax p q. +Proof. + intros R p q r H. unfold CRmin, CRmax. + setoid_replace (r * q - r * p) with (r * (q - p)). + rewrite CRabs_mult. + rewrite (CRabs_right r), <- CRmult_assoc. + apply CRmult_morph. 2: reflexivity. + rewrite CRmult_plus_distr_l, CRmult_plus_distr_l. + reflexivity. exact H. + unfold CRminus. rewrite CRmult_plus_distr_l, CRopp_mult_distr_r. reflexivity. +Qed. + +Lemma CRmin_max_mult_neg : + forall {R : ConstructiveReals} (p q r:CRcarrier R), + r <= 0 -> CRmin (r * p) (r * q) == r * CRmax p q. +Proof. + intros R p q r H. unfold CRmin, CRmax. + setoid_replace (r * q - r * p) with (r * (q - p)). + rewrite CRabs_mult. + rewrite (CRabs_left r), <- CRmult_assoc. + apply CRmult_morph. 2: reflexivity. unfold CRminus. + rewrite CRopp_mult_distr_l, CRopp_involutive, + CRmult_plus_distr_l, CRmult_plus_distr_l. + reflexivity. exact H. + unfold CRminus. rewrite CRmult_plus_distr_l, CRopp_mult_distr_r. reflexivity. +Qed. |