path: root/theories/ZArith/Zorder.v

(************************************************************************)
(*  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        *)
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(*i $Id$ i*)

(** Binary Integers (Pierre Crégut (CNET, Lannion, France) *)

Require Import BinPos.
Require Import BinInt.
Require Import Arith.
Require Import Decidable.
Require Import Zcompare.

Open Local Scope Z_scope.

Implicit Types x y z : Z.

(**********************************************************************)
(** Properties of the order relations on binary integers *)

(** Trichotomy *)

Theorem Ztrichotomy_inf : forall n m:Z, {n < m} + {n = m} + {n > m}.
Proof.
unfold Zgt, Zlt in |- *; intros m n; assert (H := refl_equal (m ?= n)).
  set (x := m ?= n) in H at 2 |- *.
  destruct x;
   [ left; right; rewrite Zcompare_Eq_eq with (1 := H) | left; left | right ];
   reflexivity.
Qed.

Theorem Ztrichotomy : forall n m:Z, n < m \/ n = m \/ n > m.
Proof.
  intros m n; destruct (Ztrichotomy_inf m n) as [[Hlt| Heq]| Hgt];
   [ left | right; left | right; right ]; assumption.
Qed.

(**********************************************************************)
(** Decidability of equality and order on Z *)

Theorem dec_eq : forall n m:Z, decidable (n = m).
Proof.
intros x y; unfold decidable in |- *; elim (Zcompare_Eq_iff_eq x y);
 intros H1 H2; elim (Dcompare (x ?= y));
 [ tauto
 | intros H3; right; unfold not in |- *; intros H4; elim H3; rewrite (H2 H4);
    intros H5; discriminate H5 ].
Qed. 

Theorem dec_Zne : forall n m:Z, decidable (Zne n m).
Proof.
intros x y; unfold decidable, Zne in |- *; elim (Zcompare_Eq_iff_eq x y).
intros H1 H2; elim (Dcompare (x ?= y));
 [ right; rewrite H1; auto
 | left; unfold not in |- *; intro; absurd ((x ?= y) = Eq);
    [ elim H; intros HR; rewrite HR; discriminate | auto ] ].
Qed.

Theorem dec_Zle : forall n m:Z, decidable (n <= m).
Proof.
intros x y; unfold decidable, Zle in |- *; elim (x ?= y);
 [ left; discriminate
 | left; discriminate
 | right; unfold not in |- *; intros H; apply H; trivial with arith ].
Qed.

Theorem dec_Zgt : forall n m:Z, decidable (n > m).
Proof.
intros x y; unfold decidable, Zgt in |- *; elim (x ?= y);
 [ right; discriminate | right; discriminate | auto with arith ].
Qed.

Theorem dec_Zge : forall n m:Z, decidable (n >= m).
Proof.
intros x y; unfold decidable, Zge in |- *; elim (x ?= y);
 [ left; discriminate
 | right; unfold not in |- *; intros H; apply H; trivial with arith
 | left; discriminate ]. 
Qed.

Theorem dec_Zlt : forall n m:Z, decidable (n < m).
Proof.
intros x y; unfold decidable, Zlt in |- *; elim (x ?= y);
 [ right; discriminate | auto with arith | right; discriminate ].
Qed.

Theorem not_Zeq : forall n m:Z, n <> m -> n < m \/ m < n.
Proof.
intros x y; elim (Dcompare (x ?= y));
 [ intros H1 H2; absurd (x = y);
    [ assumption | elim (Zcompare_Eq_iff_eq x y); auto with arith ]
 | unfold Zlt in |- *; intros H; elim H; intros H1;
    [ auto with arith
    | right; elim (Zcompare_Gt_Lt_antisym x y); auto with arith ] ].
Qed. 

(** Relating strict and large orders *)

Lemma Zgt_lt : forall n m:Z, n > m -> m < n.
Proof.
unfold Zgt, Zlt in |- *; intros m n H; elim (Zcompare_Gt_Lt_antisym m n);
 auto with arith.
Qed.

Lemma Zlt_gt : forall n m:Z, n < m -> m > n.
Proof.
unfold Zgt, Zlt in |- *; intros m n H; elim (Zcompare_Gt_Lt_antisym n m);
 auto with arith.
Qed.

Lemma Zge_le : forall n m:Z, n >= m -> m <= n.
Proof.
intros m n; change (~ m < n -> ~ n > m) in |- *; unfold not in |- *;
 intros H1 H2; apply H1; apply Zgt_lt; assumption.
Qed.

Lemma Zle_ge : forall n m:Z, n <= m -> m >= n.
Proof.
intros m n; change (~ m > n -> ~ n < m) in |- *; unfold not in |- *;
 intros H1 H2; apply H1; apply Zlt_gt; assumption.
Qed.

Lemma Zle_not_gt : forall n m:Z, n <= m -> ~ n > m.
Proof.
trivial.
Qed.

Lemma Zgt_not_le : forall n m:Z, n > m -> ~ n <= m.
Proof.
intros n m H1 H2; apply H2; assumption.
Qed.

Lemma Zle_not_lt : forall n m:Z, n <= m -> ~ m < n.
Proof.
intros n m H1 H2.
assert (H3 := Zlt_gt _ _ H2).
apply Zle_not_gt with n m; assumption.
Qed.

Lemma Zlt_not_le : forall n m:Z, n < m -> ~ m <= n.
Proof.
intros n m H1 H2.
apply Zle_not_lt with m n; assumption.
Qed.

Lemma Znot_ge_lt : forall n m:Z, ~ n >= m -> n < m.
Proof.
unfold Zge, Zlt in |- *; intros x y H; apply dec_not_not;
 [ exact (dec_Zlt x y) | assumption ].
Qed.
 
Lemma Znot_lt_ge : forall n m:Z, ~ n < m -> n >= m.
Proof.
unfold Zlt, Zge in |- *; auto with arith.
Qed.

Lemma Znot_gt_le : forall n m:Z, ~ n > m -> n <= m.
Proof.
trivial.
Qed.

Lemma Znot_le_gt : forall n m:Z, ~ n <= m -> n > m.
Proof.
unfold Zle, Zgt in |- *; intros x y H; apply dec_not_not;
 [ exact (dec_Zgt x y) | assumption ].
Qed.

Lemma Zge_iff_le : forall n m:Z, n >= m <-> m <= n.
Proof.
    intros x y; intros. split. intro. apply Zge_le. assumption.
    intro. apply Zle_ge. assumption.
Qed.

Lemma Zgt_iff_lt : forall n m:Z, n > m <-> m < n.
Proof.
    intros x y. split. intro. apply Zgt_lt. assumption.
    intro. apply Zlt_gt. assumption.
Qed.
 
(** Reflexivity *)

Lemma Zle_refl : forall n:Z, n <= n.
Proof.
intros n; unfold Zle in |- *; rewrite (Zcompare_refl n); discriminate.
Qed. 

Lemma Zeq_le : forall n m:Z, n = m -> n <= m.
Proof.
intros; rewrite H; apply Zle_refl.
Qed.

Hint Resolve Zle_refl: zarith.

(** Antisymmetry *)

Lemma Zle_antisym : forall n m:Z, n <= m -> m <= n -> n = m.
Proof.
intros n m H1 H2; destruct (Ztrichotomy n m) as [Hlt| [Heq| Hgt]]. 
  absurd (m > n); [ apply Zle_not_gt | apply Zlt_gt ]; assumption.
  assumption.
  absurd (n > m); [ apply Zle_not_gt | idtac ]; assumption.
Qed.

(** Asymmetry *)

Lemma Zgt_asym : forall n m:Z, n > m -> ~ m > n.
Proof.
unfold Zgt in |- *; intros n m H; elim (Zcompare_Gt_Lt_antisym n m);
 intros H1 H2; rewrite H1; [ discriminate | assumption ].
Qed.

Lemma Zlt_asym : forall n m:Z, n < m -> ~ m < n.
Proof.
intros n m H H1; assert (H2 : m > n). apply Zlt_gt; assumption.
assert (H3 : n > m). apply Zlt_gt; assumption.
apply Zgt_asym with m n; assumption.
Qed.

(** Irreflexivity *)

Lemma Zgt_irrefl : forall n:Z, ~ n > n.
Proof.
intros n H; apply (Zgt_asym n n H H).
Qed.

Lemma Zlt_irrefl : forall n:Z, ~ n < n.
Proof.
intros n H; apply (Zlt_asym n n H H).
Qed.

Lemma Zlt_not_eq : forall n m:Z, n < m -> n <> m.
Proof.
unfold not in |- *; intros x y H H0.
rewrite H0 in H.
apply (Zlt_irrefl _ H).
Qed.

(** Large = strict or equal *)

Lemma Zlt_le_weak : forall n m:Z, n < m -> n <= m.
Proof.
intros n m Hlt; apply Znot_gt_le; apply Zgt_asym; apply Zlt_gt; assumption.
Qed.

Lemma Zle_lt_or_eq : forall n m:Z, n <= m -> n < m \/ n = m.
Proof.
intros n m H; destruct (Ztrichotomy n m) as [Hlt| [Heq| Hgt]];
 [ left; assumption
 | right; assumption
 | absurd (n > m); [ apply Zle_not_gt | idtac ]; assumption ].
Qed.

(** Dichotomy *)

Lemma Zle_or_lt : forall n m:Z, n <= m \/ m < n.
Proof.
intros n m; destruct (Ztrichotomy n m) as [Hlt| [Heq| Hgt]];
 [ left; apply Znot_gt_le; intro Hgt; assert (Hgt' := Zlt_gt _ _ Hlt);
    apply Zgt_asym with m n; assumption
 | left; rewrite Heq; apply Zle_refl
 | right; apply Zgt_lt; assumption ].
Qed.

(** Transitivity of strict orders *)

Lemma Zgt_trans : forall n m p:Z, n > m -> m > p -> n > p.
Proof.
exact Zcompare_Gt_trans.
Qed.

Lemma Zlt_trans : forall n m p:Z, n < m -> m < p -> n < p.
Proof.
intros n m p H1 H2; apply Zgt_lt; apply Zgt_trans with (m := m); apply Zlt_gt;
 assumption.
Qed.

(** Mixed transitivity *)

Lemma Zle_gt_trans : forall n m p:Z, m <= n -> m > p -> n > p.
Proof.
intros n m p H1 H2; destruct (Zle_lt_or_eq m n H1) as [Hlt| Heq];
 [ apply Zgt_trans with m; [ apply Zlt_gt; assumption | assumption ]
 | rewrite <- Heq; assumption ].
Qed.

Lemma Zgt_le_trans : forall n m p:Z, n > m -> p <= m -> n > p.
Proof.
intros n m p H1 H2; destruct (Zle_lt_or_eq p m H2) as [Hlt| Heq];
 [ apply Zgt_trans with m; [ assumption | apply Zlt_gt; assumption ]
 | rewrite Heq; assumption ].
Qed.

Lemma Zlt_le_trans : forall n m p:Z, n < m -> m <= p -> n < p.
intros n m p H1 H2; apply Zgt_lt; apply Zle_gt_trans with (m := m);
 [ assumption | apply Zlt_gt; assumption ].
Qed.

Lemma Zle_lt_trans : forall n m p:Z, n <= m -> m < p -> n < p.
Proof.
intros n m p H1 H2; apply Zgt_lt; apply Zgt_le_trans with (m := m);
 [ apply Zlt_gt; assumption | assumption ].
Qed.

(** Transitivity of large orders *)

Lemma Zle_trans : forall n m p:Z, n <= m -> m <= p -> n <= p.
Proof.
intros n m p H1 H2; apply Znot_gt_le.
intro Hgt; apply Zle_not_gt with n m. assumption.
exact (Zgt_le_trans n p m Hgt H2).
Qed.

Lemma Zge_trans : forall n m p:Z, n >= m -> m >= p -> n >= p.
Proof.
intros n m p H1 H2.
apply Zle_ge.
apply Zle_trans with m; apply Zge_le; trivial.
Qed.

Hint Resolve Zle_trans: zarith.

(** Compatibility of successor wrt to order *)

Lemma Zsucc_le_compat : forall n m:Z, m <= n -> Zsucc m <= Zsucc n.
Proof.
unfold Zle, not in |- *; intros m n H1 H2; apply H1;
 rewrite <- (Zcompare_plus_compat n m 1); do 2 rewrite (Zplus_comm 1);
 exact H2.
Qed.

Lemma Zsucc_gt_compat : forall n m:Z, m > n -> Zsucc m > Zsucc n.
Proof.
unfold Zgt in |- *; intros n m H; rewrite Zcompare_succ_compat;
 auto with arith.
Qed.

Lemma Zsucc_lt_compat : forall n m:Z, n < m -> Zsucc n < Zsucc m.
Proof.
intros n m H; apply Zgt_lt; apply Zsucc_gt_compat; apply Zlt_gt; assumption.
Qed.

Hint Resolve Zsucc_le_compat: zarith.

(** Simplification of successor wrt to order *)

Lemma Zsucc_gt_reg : forall n m:Z, Zsucc m > Zsucc n -> m > n.
Proof.
unfold Zsucc, Zgt in |- *; intros n p;
 do 2 rewrite (fun m:Z => Zplus_comm m 1);
 rewrite (Zcompare_plus_compat p n 1); trivial with arith.
Qed.

Lemma Zsucc_le_reg : forall n m:Z, Zsucc m <= Zsucc n -> m <= n.
Proof.
unfold Zle, not in |- *; intros m n H1 H2; apply H1; unfold Zsucc in |- *;
 do 2 rewrite <- (Zplus_comm 1); rewrite (Zcompare_plus_compat n m 1);
 assumption.
Qed.

Lemma Zsucc_lt_reg : forall n m:Z, Zsucc n < Zsucc m -> n < m.
Proof.
intros n m H; apply Zgt_lt; apply Zsucc_gt_reg; apply Zlt_gt; assumption.
Qed.

(** Compatibility of addition wrt to order *)

Lemma Zplus_gt_compat_l : forall n m p:Z, n > m -> p + n > p + m.
Proof.
unfold Zgt in |- *; intros n m p H; rewrite (Zcompare_plus_compat n m p);
 assumption.
Qed.

Lemma Zplus_gt_compat_r : forall n m p:Z, n > m -> n + p > m + p.
Proof.
intros n m p H; rewrite (Zplus_comm n p); rewrite (Zplus_comm m p);
 apply Zplus_gt_compat_l; trivial.
Qed.

Lemma Zplus_le_compat_l : forall n m p:Z, n <= m -> p + n <= p + m.
Proof.
intros n m p; unfold Zle, not in |- *; intros H1 H2; apply H1;
 rewrite <- (Zcompare_plus_compat n m p); assumption.
Qed.

Lemma Zplus_le_compat_r : forall n m p:Z, n <= m -> n + p <= m + p.
Proof.
intros a b c; do 2 rewrite (fun n:Z => Zplus_comm n c);
 exact (Zplus_le_compat_l a b c).
Qed.

Lemma Zplus_lt_compat_l : forall n m p:Z, n < m -> p + n < p + m.
Proof.
unfold Zlt in |- *; intros n m p; rewrite Zcompare_plus_compat;
 trivial with arith.
Qed.

Lemma Zplus_lt_compat_r : forall n m p:Z, n < m -> n + p < m + p.
Proof.
intros n m p H; rewrite (Zplus_comm n p); rewrite (Zplus_comm m p);
 apply Zplus_lt_compat_l; trivial.
Qed.

Lemma Zplus_lt_le_compat : forall n m p q:Z, n < m -> p <= q -> n + p < m + q.
Proof.
intros a b c d H0 H1.
apply Zlt_le_trans with (b + c).
apply Zplus_lt_compat_r; trivial.
apply Zplus_le_compat_l; trivial.
Qed.

Lemma Zplus_le_lt_compat : forall n m p q:Z, n <= m -> p < q -> n + p < m + q.
Proof.
intros a b c d H0 H1.
apply Zle_lt_trans with (b + c).
apply Zplus_le_compat_r; trivial.
apply Zplus_lt_compat_l; trivial.
Qed.

Lemma Zplus_le_compat : forall n m p q:Z, n <= m -> p <= q -> n + p <= m + q.
Proof.
intros n m p q; intros H1 H2; apply Zle_trans with (m := n + q);
 [ apply Zplus_le_compat_l; assumption
 | apply Zplus_le_compat_r; assumption ].
Qed.


Lemma Zplus_lt_compat : forall n m p q:Z, n < m -> p < q -> n + p < m + q.
intros; apply Zplus_le_lt_compat. apply Zlt_le_weak; assumption. assumption.
Qed.


(** Compatibility of addition wrt to being positive *)

Lemma Zplus_le_0_compat : forall n m:Z, 0 <= n -> 0 <= m -> 0 <= n + m.
Proof.
intros x y H1 H2; rewrite <- (Zplus_0_l 0); apply Zplus_le_compat; assumption.
Qed.

(** Simplification of addition wrt to order *)

Lemma Zplus_gt_reg_l : forall n m p:Z, p + n > p + m -> n > m.
Proof.
unfold Zgt in |- *; intros n m p H; rewrite <- (Zcompare_plus_compat n m p);
 assumption.
Qed.

Lemma Zplus_gt_reg_r : forall n m p:Z, n + p > m + p -> n > m.
Proof.
intros n m p H; apply Zplus_gt_reg_l with p.
rewrite (Zplus_comm p n); rewrite (Zplus_comm p m); trivial.
Qed.

Lemma Zplus_le_reg_l : forall n m p:Z, p + n <= p + m -> n <= m.
Proof.
intros n m p; unfold Zle, not in |- *; intros H1 H2; apply H1;
 rewrite (Zcompare_plus_compat n m p); assumption.
Qed.
 
Lemma Zplus_le_reg_r : forall n m p:Z, n + p <= m + p -> n <= m.
Proof.
intros n m p H; apply Zplus_le_reg_l with p.
rewrite (Zplus_comm p n); rewrite (Zplus_comm p m); trivial.
Qed.

Lemma Zplus_lt_reg_l : forall n m p:Z, p + n < p + m -> n < m.
Proof.
unfold Zlt in |- *; intros n m p; rewrite Zcompare_plus_compat;
 trivial with arith.
Qed.
 
Lemma Zplus_lt_reg_r : forall n m p:Z, n + p < m + p -> n < m.
Proof.
intros n m p H; apply Zplus_lt_reg_l with p.
rewrite (Zplus_comm p n); rewrite (Zplus_comm p m); trivial.
Qed.
 
(** Special base instances of order *)

Lemma Zgt_succ : forall n:Z, Zsucc n > n.
Proof.
exact Zcompare_succ_Gt.
Qed.

Lemma Znot_le_succ : forall n:Z, ~ Zsucc n <= n.
Proof.
intros n; apply Zgt_not_le; apply Zgt_succ.
Qed.

Lemma Zlt_succ : forall n:Z, n < Zsucc n.
Proof.
intro n; apply Zgt_lt; apply Zgt_succ.
Qed.

Lemma Zlt_pred : forall n:Z, Zpred n < n.
Proof.
intros n; apply Zsucc_lt_reg; rewrite <- Zsucc_pred; apply Zlt_succ.
Qed.

(** Relating strict and large order using successor or predecessor *)

Lemma Zgt_le_succ : forall n m:Z, m > n -> Zsucc n <= m.
Proof.
unfold Zgt, Zle in |- *; intros n p H; elim (Zcompare_Gt_not_Lt p n);
 intros H1 H2; unfold not in |- *; intros H3; unfold not in H1; 
 apply H1;
 [ assumption
 | elim (Zcompare_Gt_Lt_antisym (n + 1) p); intros H4 H5; apply H4; exact H3 ].
Qed.

Lemma Zlt_gt_succ : forall n m:Z, n <= m -> Zsucc m > n.
Proof.
intros n p H; apply Zgt_le_trans with p.
  apply Zgt_succ.
  assumption.
Qed.

Lemma Zle_lt_succ : forall n m:Z, n <= m -> n < Zsucc m.
Proof.
intros n m H; apply Zgt_lt; apply Zlt_gt_succ; assumption.
Qed.

Lemma Zlt_le_succ : forall n m:Z, n < m -> Zsucc n <= m.
Proof.
intros n p H; apply Zgt_le_succ; apply Zlt_gt; assumption.
Qed.

Lemma Zgt_succ_le : forall n m:Z, Zsucc m > n -> n <= m.
Proof.
intros n p H; apply Zsucc_le_reg; apply Zgt_le_succ; assumption.
Qed.

Lemma Zlt_succ_le : forall n m:Z, n < Zsucc m -> n <= m.
Proof.
intros n m H; apply Zgt_succ_le; apply Zlt_gt; assumption.
Qed.

Lemma Zlt_succ_gt : forall n m:Z, Zsucc n <= m -> m > n.
Proof.
intros n m H; apply Zle_gt_trans with (m := Zsucc n);
 [ assumption | apply Zgt_succ ].
Qed.

(** Weakening order *)

Lemma Zle_succ : forall n:Z, n <= Zsucc n.
Proof.
intros n; apply Zgt_succ_le; apply Zgt_trans with (m := Zsucc n);
 apply Zgt_succ.
Qed.

Hint Resolve Zle_succ: zarith.

Lemma Zle_pred : forall n:Z, Zpred n <= n.
Proof.
intros n; pattern n at 2 in |- *; rewrite Zsucc_pred; apply Zle_succ.
Qed.

Lemma Zlt_lt_succ : forall n m:Z, n < m -> n < Zsucc m.
intros n m H; apply Zgt_lt; apply Zgt_trans with (m := m);
 [ apply Zgt_succ | apply Zlt_gt; assumption ].
Qed.

Lemma Zle_le_succ : forall n m:Z, n <= m -> n <= Zsucc m.
Proof.
intros x y H.
apply Zle_trans with y; trivial with zarith.
Qed.

Lemma Zle_succ_le : forall n m:Z, Zsucc n <= m -> n <= m.
Proof.
intros n m H; apply Zle_trans with (m := Zsucc n);
 [ apply Zle_succ | assumption ].
Qed.

Hint Resolve Zle_le_succ: zarith.

(** Relating order wrt successor and order wrt predecessor *)

Lemma Zgt_succ_pred : forall n m:Z, m > Zsucc n -> Zpred m > n.
Proof.
unfold Zgt, Zsucc, Zpred in |- *; intros n p H;
 rewrite <- (fun x y => Zcompare_plus_compat x y 1); 
 rewrite (Zplus_comm p); rewrite Zplus_assoc;
 rewrite (fun x => Zplus_comm x n); simpl in |- *; 
 assumption.
Qed.

Lemma Zlt_succ_pred : forall n m:Z, Zsucc n < m -> n < Zpred m.
Proof.
intros n p H; apply Zsucc_lt_reg; rewrite <- Zsucc_pred; assumption.
Qed.

(** Relating strict order and large order on positive *)

Lemma Zlt_0_le_0_pred : forall n:Z, 0 < n -> 0 <= Zpred n.
intros x H.
rewrite (Zsucc_pred x) in H.
apply Zgt_succ_le.
apply Zlt_gt.
assumption.
Qed.


Lemma Zgt_0_le_0_pred : forall n:Z, n > 0 -> 0 <= Zpred n.
intros; apply Zlt_0_le_0_pred; apply Zgt_lt. assumption.
Qed.


(** Special cases of ordered integers *)

Lemma Zlt_0_1 : 0 < 1.
Proof.
change (0 < Zsucc 0) in |- *. apply Zlt_succ.
Qed.

Lemma Zle_0_1 : 0 <= 1.
Proof.
change (0 <= Zsucc 0) in |- *. apply Zle_succ.
Qed.

Lemma Zle_neg_pos : forall p q:positive, Zneg p <= Zpos q.
Proof.
intros p; red in |- *; simpl in |- *; red in |- *; intros H; discriminate.
Qed.

Lemma Zgt_pos_0 : forall p:positive, Zpos p > 0.
unfold Zgt in |- *; trivial.
Qed.

  (* weaker but useful (in [Zpower] for instance) *)
Lemma Zle_0_pos : forall p:positive, 0 <= Zpos p.
intro; unfold Zle in |- *; discriminate.
Qed.

Lemma Zlt_neg_0 : forall p:positive, Zneg p < 0.
unfold Zlt in |- *; trivial.
Qed.

Lemma Zle_0_nat : forall n:nat, 0 <= Z_of_nat n.
simple induction n; simpl in |- *; intros;
 [ apply Zle_refl | unfold Zle in |- *; simpl in |- *; discriminate ].
Qed.

Hint Immediate Zeq_le: zarith.

(** Transitivity using successor *)

Lemma Zge_trans_succ : forall n m p:Z, Zsucc n > m -> m > p -> n > p.
Proof.
intros n m p H1 H2; apply Zle_gt_trans with (m := m);
 [ apply Zgt_succ_le; assumption | assumption ].
Qed.

(** Derived lemma *)

Lemma Zgt_succ_gt_or_eq : forall n m:Z, Zsucc n > m -> n > m \/ m = n.
Proof.
intros n m H.
assert (Hle : m <= n).
  apply Zgt_succ_le; assumption.
destruct (Zle_lt_or_eq _ _ Hle) as [Hlt| Heq].
  left; apply Zlt_gt; assumption.  
  right; assumption.
Qed.

(** Compatibility of multiplication by a positive wrt to order *)


Lemma Zmult_le_compat_r : forall n m p:Z, n <= m -> 0 <= p -> n * p <= m * p.
Proof.
intros a b c H H0; destruct c.
  do 2 rewrite Zmult_0_r; assumption.
  rewrite (Zmult_comm a); rewrite (Zmult_comm b).
    unfold Zle in |- *; rewrite Zcompare_mult_compat; assumption.
  unfold Zle in H0; contradiction H0; reflexivity.
Qed.

Lemma Zmult_le_compat_l : forall n m p:Z, n <= m -> 0 <= p -> p * n <= p * m.
Proof.
intros a b c H1 H2; rewrite (Zmult_comm c a); rewrite (Zmult_comm c b).
apply Zmult_le_compat_r; trivial.
Qed.

Lemma Zmult_lt_compat_r : forall n m p:Z, 0 < p -> n < m -> n * p < m * p.
Proof.
intros x y z H H0; destruct z.
  contradiction (Zlt_irrefl 0).
  rewrite (Zmult_comm x); rewrite (Zmult_comm y).
    unfold Zlt in |- *; rewrite Zcompare_mult_compat; assumption.
  discriminate H.
Qed.

Lemma Zmult_gt_compat_r : forall n m p:Z, p > 0 -> n > m -> n * p > m * p.
Proof.
intros x y z; intros; apply Zlt_gt; apply Zmult_lt_compat_r; apply Zgt_lt;
 assumption.
Qed.

Lemma Zmult_gt_0_lt_compat_r :
 forall n m p:Z, p > 0 -> n < m -> n * p < m * p.
Proof.
intros x y z; intros; apply Zmult_lt_compat_r;
 [ apply Zgt_lt; assumption | assumption ].
Qed.

Lemma Zmult_gt_0_le_compat_r :
 forall n m p:Z, p > 0 -> n <= m -> n * p <= m * p.
Proof.
intros x y z Hz Hxy.
elim (Zle_lt_or_eq x y Hxy).
intros; apply Zlt_le_weak.
apply Zmult_gt_0_lt_compat_r; trivial.
intros; apply Zeq_le.
rewrite H; trivial.
Qed.

Lemma Zmult_lt_0_le_compat_r :
 forall n m p:Z, 0 < p -> n <= m -> n * p <= m * p.
Proof.
intros x y z; intros; apply Zmult_gt_0_le_compat_r; try apply Zlt_gt;
 assumption.
Qed.

Lemma Zmult_gt_0_lt_compat_l :
 forall n m p:Z, p > 0 -> n < m -> p * n < p * m.
Proof.
intros x y z; intros.
rewrite (Zmult_comm z x); rewrite (Zmult_comm z y);
 apply Zmult_gt_0_lt_compat_r; assumption.
Qed.

Lemma Zmult_lt_compat_l : forall n m p:Z, 0 < p -> n < m -> p * n < p * m.
Proof.
intros x y z; intros.
rewrite (Zmult_comm z x); rewrite (Zmult_comm z y);
 apply Zmult_gt_0_lt_compat_r; try apply Zlt_gt; assumption.
Qed.

Lemma Zmult_gt_compat_l : forall n m p:Z, p > 0 -> n > m -> p * n > p * m.
Proof.
intros x y z; intros; rewrite (Zmult_comm z x); rewrite (Zmult_comm z y);
 apply Zmult_gt_compat_r; assumption.
Qed.

Lemma Zmult_ge_compat_r : forall n m p:Z, n >= m -> p >= 0 -> n * p >= m * p.
Proof.
intros a b c H1 H2; apply Zle_ge.
apply Zmult_le_compat_r; apply Zge_le; trivial.
Qed.

Lemma Zmult_ge_compat_l : forall n m p:Z, n >= m -> p >= 0 -> p * n >= p * m.
Proof.
intros a b c H1 H2; apply Zle_ge.
apply Zmult_le_compat_l; apply Zge_le; trivial.
Qed.

Lemma Zmult_ge_compat :
 forall n m p q:Z, n >= p -> m >= q -> p >= 0 -> q >= 0 -> n * m >= p * q.
Proof.
intros a b c d H0 H1 H2 H3.
apply Zge_trans with (a * d).
apply Zmult_ge_compat_l; trivial.
apply Zge_trans with c; trivial. 
apply Zmult_ge_compat_r; trivial.
Qed.

Lemma Zmult_le_compat :
 forall n m p q:Z, n <= p -> m <= q -> 0 <= n -> 0 <= m -> n * m <= p * q.
Proof.
intros a b c d H0 H1 H2 H3.
apply Zle_trans with (c * b).
apply Zmult_le_compat_r; assumption.
apply Zmult_le_compat_l.
assumption.
apply Zle_trans with a; assumption.
Qed.

(** Simplification of multiplication by a positive wrt to being positive *)

Lemma Zmult_gt_0_lt_reg_r : forall n m p:Z, p > 0 -> n * p < m * p -> n < m.
Proof.
intros x y z; intros; destruct z.
  contradiction (Zgt_irrefl 0).
  rewrite (Zmult_comm x) in H0; rewrite (Zmult_comm y) in H0.
    unfold Zlt in H0; rewrite Zcompare_mult_compat in H0; assumption.
  discriminate H.
Qed.

Lemma Zmult_lt_reg_r : forall n m p:Z, 0 < p -> n * p < m * p -> n < m.
Proof.
intros a b c H0 H1.
apply Zmult_gt_0_lt_reg_r with c; try apply Zlt_gt; assumption.
Qed.

Lemma Zmult_le_reg_r : forall n m p:Z, p > 0 -> n * p <= m * p -> n <= m.
Proof.
intros x y z Hz Hxy.
elim (Zle_lt_or_eq (x * z) (y * z) Hxy).
intros; apply Zlt_le_weak.
apply Zmult_gt_0_lt_reg_r with z; trivial.
intros; apply Zeq_le.
apply Zmult_reg_r with z.
  intro. rewrite H0 in Hz. contradiction (Zgt_irrefl 0).
assumption.
Qed.

Lemma Zmult_lt_0_le_reg_r : forall n m p:Z, 0 < p -> n * p <= m * p -> n <= m.
intros x y z; intros; apply Zmult_le_reg_r with z.
try apply Zlt_gt; assumption.
assumption.
Qed.


Lemma Zmult_ge_reg_r : forall n m p:Z, p > 0 -> n * p >= m * p -> n >= m.
intros a b c H1 H2; apply Zle_ge; apply Zmult_le_reg_r with c; trivial.
apply Zge_le; trivial.
Qed.

Lemma Zmult_gt_reg_r : forall n m p:Z, p > 0 -> n * p > m * p -> n > m.
intros a b c H1 H2; apply Zlt_gt; apply Zmult_gt_0_lt_reg_r with c; trivial.
apply Zgt_lt; trivial.
Qed.


(** Compatibility of multiplication by a positive wrt to being positive *)

Lemma Zmult_le_0_compat : forall n m:Z, 0 <= n -> 0 <= m -> 0 <= n * m.
Proof.
intros x y; case x.
intros; rewrite Zmult_0_l; trivial.
intros p H1; unfold Zle in |- *.
  pattern 0 at 2 in |- *; rewrite <- (Zmult_0_r (Zpos p)).
  rewrite Zcompare_mult_compat; trivial.
intros p H1 H2; absurd (0 > Zneg p); trivial.
unfold Zgt in |- *; simpl in |- *; auto with zarith.
Qed.

Lemma Zmult_gt_0_compat : forall n m:Z, n > 0 -> m > 0 -> n * m > 0.
Proof.
intros x y; case x.
intros H; discriminate H.
intros p H1; unfold Zgt in |- *; pattern 0 at 2 in |- *;
 rewrite <- (Zmult_0_r (Zpos p)).
  rewrite Zcompare_mult_compat; trivial.
intros p H; discriminate H.
Qed.

Lemma Zmult_lt_0_compat : forall n m:Z, 0 < n -> 0 < m -> 0 < n * m.
intros a b apos bpos.
apply Zgt_lt.
apply Zmult_gt_0_compat; try apply Zlt_gt; assumption.
Qed.

(* For compatibility *)
Notation Zmult_lt_O_compat := Zmult_lt_0_compat (only parsing).

Lemma Zmult_gt_0_le_0_compat : forall n m:Z, n > 0 -> 0 <= m -> 0 <= m * n.
Proof.
intros x y H1 H2; apply Zmult_le_0_compat; trivial.
apply Zlt_le_weak; apply Zgt_lt; trivial.
Qed.

(** Simplification of multiplication by a positive wrt to being positive *)

Lemma Zmult_le_0_reg_r : forall n m:Z, n > 0 -> 0 <= m * n -> 0 <= m.
Proof.
intros x y; case x;
 [ simpl in |- *; unfold Zgt in |- *; simpl in |- *; intros H; discriminate H
 | intros p H1; unfold Zle in |- *; rewrite Zmult_comm;
    pattern 0 at 1 in |- *; rewrite <- (Zmult_0_r (Zpos p));
    rewrite Zcompare_mult_compat; auto with arith
 | intros p; unfold Zgt in |- *; simpl in |- *; intros H; discriminate H ].
Qed.

Lemma Zmult_gt_0_lt_0_reg_r : forall n m:Z, n > 0 -> 0 < m * n -> 0 < m.
Proof.
intros x y; case x;
 [ simpl in |- *; unfold Zgt in |- *; simpl in |- *; intros H; discriminate H
 | intros p H1; unfold Zlt in |- *; rewrite Zmult_comm;
    pattern 0 at 1 in |- *; rewrite <- (Zmult_0_r (Zpos p));
    rewrite Zcompare_mult_compat; auto with arith
 | intros p; unfold Zgt in |- *; simpl in |- *; intros H; discriminate H ].
Qed.

Lemma Zmult_lt_0_reg_r : forall n m:Z, 0 < n -> 0 < m * n -> 0 < m.
Proof.
intros x y; intros; eapply Zmult_gt_0_lt_0_reg_r with x; try apply Zlt_gt;
 assumption.
Qed.

Lemma Zmult_gt_0_reg_l : forall n m:Z, n > 0 -> n * m > 0 -> m > 0.
Proof.
intros x y; case x.
 intros H; discriminate H.
 intros p H1; unfold Zgt in |- *.
 pattern 0 at 1 in |- *; rewrite <- (Zmult_0_r (Zpos p)).
 rewrite Zcompare_mult_compat; trivial.
intros p H; discriminate H.
Qed.

(** Simplification of square wrt order *)

Lemma Zgt_square_simpl :
 forall n m:Z, n >= 0 -> n * n > m * m -> n > m.
Proof.
intros n m H0 H1.
case (dec_Zlt m n).
intro; apply Zlt_gt; trivial.
intros H2; cut (m >= n).
intros H.
elim Zgt_not_le with (1 := H1).
apply Zge_le.
apply Zmult_ge_compat; auto.
apply Znot_lt_ge; trivial.
Qed.

Lemma Zlt_square_simpl :
 forall n m:Z, 0 <= n -> m * m < n * n -> m < n.
Proof.
intros x y H0 H1.
apply Zgt_lt.
apply Zgt_square_simpl; try apply Zle_ge; try apply Zlt_gt; assumption.
Qed.

(** Equivalence between inequalities *)

Lemma Zle_plus_swap : forall n m p:Z, n + p <= m <-> n <= m - p.
Proof.
    intros x y z; intros. split. intro. rewrite <- (Zplus_0_r x). rewrite <- (Zplus_opp_r z).
    rewrite Zplus_assoc. exact (Zplus_le_compat_r _ _ _ H).
    intro. rewrite <- (Zplus_0_r y). rewrite <- (Zplus_opp_l z). rewrite Zplus_assoc.
    apply Zplus_le_compat_r. assumption.
Qed.

Lemma Zlt_plus_swap : forall n m p:Z, n + p < m <-> n < m - p.
Proof.
    intros x y z; intros. split. intro. unfold Zminus in |- *. rewrite Zplus_comm. rewrite <- (Zplus_0_l x).
    rewrite <- (Zplus_opp_l z). rewrite Zplus_assoc_reverse. apply Zplus_lt_compat_l. rewrite Zplus_comm.
    assumption.
    intro. rewrite Zplus_comm. rewrite <- (Zplus_0_l y). rewrite <- (Zplus_opp_r z).
    rewrite Zplus_assoc_reverse. apply Zplus_lt_compat_l. rewrite Zplus_comm. assumption.
Qed.

Lemma Zeq_plus_swap : forall n m p:Z, n + p = m <-> n = m - p.
Proof.
intros x y z; intros. split. intro. apply Zplus_minus_eq. symmetry  in |- *. rewrite Zplus_comm. 
  assumption.
intro. rewrite H. unfold Zminus in |- *. rewrite Zplus_assoc_reverse. 
  rewrite Zplus_opp_l. apply Zplus_0_r.
Qed.

Lemma Zlt_minus_simpl_swap : forall n m:Z, 0 < m -> n - m < n.
Proof.
intros n m H; apply Zplus_lt_reg_l with (p := m); rewrite Zplus_minus;
 pattern n at 1 in |- *; rewrite <- (Zplus_0_r n); 
 rewrite (Zplus_comm m n); apply Zplus_lt_compat_l; 
 assumption.
Qed.

Lemma Zlt_0_minus_lt : forall n m:Z, 0 < n - m -> m < n.
Proof.
intros n m H; apply Zplus_lt_reg_l with (p := - m); rewrite Zplus_opp_l;
 rewrite Zplus_comm; exact H.
Qed.

(* For compatibility *)
Notation Zlt_O_minus_lt := Zlt_0_minus_lt (only parsing).