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(*  The Why3 Verification Platform   /   The Why3 Development Team  *)
(*  Copyright 2010-2023 --  Inria - CNRS - Paris-Saclay University  *)
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(*  This software is distributed under the terms of the GNU Lesser  *)
(*  General Public License version 2.1, with the special exception  *)
(*  on linking described in file LICENSE.                           *)
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(* This file is generated by Why3's Coq-realize driver *)
(* Beware! Only edit allowed sections below    *)
Require Import BuiltIn.
Require BuiltIn.
Require int.Int.
Require int.Abs.
Require int.EuclideanDivision.
Require int.ComputerDivision.
Require number.Parity.

(* Hack so that Why3 does not override the notation below.

(* Why3 assumption *)
Definition divides (d:Numbers.BinNums.Z) (n:Numbers.BinNums.Z) : Prop :=
  ((d = 0%Z) -> (n = 0%Z)) /\
  (~ (d = 0%Z) -> ((ZArith.BinInt.Z.rem n d) = 0%Z)).

(* Why3 goal *)
Lemma divides'spec :
  forall (d:Numbers.BinNums.Z) (n:Numbers.BinNums.Z),
  divides d n <-> (exists q:Numbers.BinNums.Z, (n = (q * d)%Z)).
Proof.
intros d n.

Qed.

*)

Require Import Znumtheory.
Notation divides := Z.divide (only parsing).

(* Why3 goal *)
Lemma divides_refl : forall (n:Numbers.BinNums.Z), divides n n.
Proof.
exact Z.divide_refl.
Qed.

(* Why3 goal *)
Lemma divides_1_n : forall (n:Numbers.BinNums.Z), divides 1%Z n.
Proof.
exact Zone_divide.
Qed.

(* Why3 goal *)
Lemma divides_0 : forall (n:Numbers.BinNums.Z), divides n 0%Z.
Proof.
exact Zdivide_0.
Qed.

(* Why3 goal *)
Lemma divides_left :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z) (c:Numbers.BinNums.Z),
  divides a b -> divides (c * a)%Z (c * b)%Z.
Proof.
exact Zmult_divide_compat_l.
Qed.

(* Why3 goal *)
Lemma divides_right :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z) (c:Numbers.BinNums.Z),
  divides a b -> divides (a * c)%Z (b * c)%Z.
Proof.
exact Zmult_divide_compat_r.
Qed.

(* Why3 goal *)
Lemma divides_oppr :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), divides a b ->
  divides a (-b)%Z.
Proof.
exact Zdivide_opp_r.
Qed.

(* Why3 goal *)
Lemma divides_oppl :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), divides a b ->
  divides (-a)%Z b.
Proof.
exact Zdivide_opp_l.
Qed.

(* Why3 goal *)
Lemma divides_oppr_rev :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), divides (-a)%Z b ->
  divides a b.
Proof.
exact Zdivide_opp_l_rev.
Qed.

(* Why3 goal *)
Lemma divides_oppl_rev :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), divides a (-b)%Z ->
  divides a b.
Proof.
exact Zdivide_opp_r_rev.
Qed.

(* Why3 goal *)
Lemma divides_plusr :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z) (c:Numbers.BinNums.Z),
  divides a b -> divides a c -> divides a (b + c)%Z.
Proof.
exact Zdivide_plus_r.
Qed.

(* Why3 goal *)
Lemma divides_minusr :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z) (c:Numbers.BinNums.Z),
  divides a b -> divides a c -> divides a (b - c)%Z.
Proof.
exact Zdivide_minus_l.
Qed.

(* Why3 goal *)
Lemma divides_multl :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z) (c:Numbers.BinNums.Z),
  divides a b -> divides a (c * b)%Z.
Proof.
intros a b c.
apply Zdivide_mult_r.
Qed.

(* Why3 goal *)
Lemma divides_multr :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z) (c:Numbers.BinNums.Z),
  divides a b -> divides a (b * c)%Z.
Proof.
exact Zdivide_mult_l.
Qed.

(* Why3 goal *)
Lemma divides_factorl :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), divides a (b * a)%Z.
Proof.
exact Zdivide_factor_l.
Qed.

(* Why3 goal *)
Lemma divides_factorr :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), divides a (a * b)%Z.
Proof.
exact Zdivide_factor_r.
Qed.

(* Why3 goal *)
Lemma divides_n_1 :
  forall (n:Numbers.BinNums.Z), divides n 1%Z -> (n = 1%Z) \/ (n = (-1%Z)%Z).
Proof.
exact Zdivide_1.
Qed.

(* Why3 goal *)
Lemma divides_antisym :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), divides a b ->
  divides b a -> (a = b) \/ (a = (-b)%Z).
Proof.
exact Z.divide_antisym.
Qed.

(* Why3 goal *)
Lemma divides_trans :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z) (c:Numbers.BinNums.Z),
  divides a b -> divides b c -> divides a c.
Proof.
exact Z.divide_trans.
Qed.

(* Why3 goal *)
Lemma divides_bounds :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), divides a b ->
  ~ (b = 0%Z) -> ((ZArith.BinInt.Z.abs a) <= (ZArith.BinInt.Z.abs b))%Z.
Proof.
exact Zdivide_bounds.
Qed.

Import EuclideanDivision.

(* Why3 goal *)
Lemma mod_divides_euclidean :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), ~ (b = 0%Z) ->
  ((int.EuclideanDivision.mod1 a b) = 0%Z) -> divides b a.
Proof.
intros a b Zb H.
exists (div a b).
rewrite (Div_mod a b Zb) at 1.
rewrite H.
ring.
Qed.

(* Why3 goal *)
Lemma divides_mod_euclidean :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), ~ (b = 0%Z) ->
  divides b a -> ((int.EuclideanDivision.mod1 a b) = 0%Z).
Proof.
intros a b Zb H.
assert (Zmod a b = Z0).
now apply Zdivide_mod.
unfold mod1, div.
rewrite H0.
case Z_le_dec ; intros H1.
rewrite (Z_div_exact_full_2 a b Zb H0) at 1.
apply Zminus_diag.
now elim H1.
Qed.

(* Why3 goal *)
Lemma mod_divides_computer :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), ~ (b = 0%Z) ->
  ((ZArith.BinInt.Z.rem a b) = 0%Z) -> divides b a.
Proof.
intros a b Zb H.
exists (Z.quot a b).
rewrite Zmult_comm.
now apply Zquot.Z_quot_exact_full.
Qed.

(* Why3 goal *)
Lemma divides_mod_computer :
  forall (a:Numbers.BinNums.Z) (b:Numbers.BinNums.Z), ~ (b = 0%Z) ->
  divides b a -> ((ZArith.BinInt.Z.rem a b) = 0%Z).
Proof.
intros a b Zb (q,H).
rewrite H.
apply Zquot.Z_rem_mult.
Qed.

(* Why3 goal *)
Lemma even_divides :
  forall (a:Numbers.BinNums.Z), number.Parity.even a <-> divides 2%Z a.
Proof.
split ;
  intros (q,H) ; exists q ; now rewrite Zmult_comm.
Qed.

(* Why3 goal *)
Lemma odd_divides :
  forall (a:Numbers.BinNums.Z), number.Parity.odd a <-> ~ divides 2%Z a.
Proof.
split.
intros H.
contradict H.
apply Parity.even_not_odd.
now apply <- even_divides.
intros H.
destruct (Parity.even_or_odd a).
elim H.
now apply -> even_divides.
exact H0.
Qed.

