(* Contribution to the Coq Library   V6.3 (July 1999)                    *)
(****************************************************************************)
(*                 The Calculus of Inductive Constructions                  *)
(*                                                                          *)
(*                                Projet Coq                                *)
(*                                                                          *)
(*                     INRIA                        ENS-CNRS                *)
(*              Rocquencourt                        Lyon                    *)
(*                                                                          *)
(*                                Coq V5.10                                 *)
(*                              Nov 25th 1994                               *)
(*                                                                          *)
(****************************************************************************)
(*                                 Zmult.v                                  *)
(****************************************************************************)
Require Export Lci.
Require Export misc.
Require Export Arith.
Require Export Nat_complements.
Require Export groups.
Require Export rings.
Require Export Zbase.
Require Export Z_succ_pred.
Require Export Zadd.
(* Multiplication on Z, (Z, +, *, 0, 1) is a unitary commutative ring *)
(*Recursive Definition multZ : Z -> Z -> Z := OZ      y  => OZ | (pos O)      y  => y | (pos (S n1)) y  => (addZ (multZ (pos n1) y) y) | (neg O)      y  => (oppZ y) | (neg (S n1)) y  => (addZ (multZ (neg n1) y) (oppZ y)). *)
Fixpoint multpos (x2 : Z) (n : nat) {struct n} : Z :=
match n with
| O => x2
| S n0 => addZ (multpos x2 n0) x2
end.
Fixpoint multneg (x2 : Z) (n : nat) {struct n} : Z :=
match n with
| O => oppZ x2
| S n0 => addZ (multneg x2 n0) (oppZ x2)
end.
Definition multZ (x1 x2 : Z) :=
match x1 with
| OZ => OZ
| pos n => multpos x2 n
| neg n => multneg x2 n
end.
Proof multZ_eq3.
Proof multZ_eq5.
intros; elim x.
(* OZ *)
simpl in |- *; reflexivity.
(* pos n *)
intros; simpl in |- *; reflexivity.
(* neg n *)
intros; elim n.
(* neg O *)
simpl in |- *; symmetry  in |- *.
elim (addZ_opposite y I); intros. elim H0; intros; elim H2; intros; exact H4.
(* neg (S n0) *)
intros; unfold succZ in |- *; rewrite (tech_mult_negZ n0 y).
elim (addZ_associativity (multZ (neg n0) y) (oppZ y) y).
elim (addZ_opposite y I); intros. elim H1; intros; elim H3; intros. rewrite H5.
symmetry  in |- *; exact (add_OZ (multZ (neg n0) y)).
Qed.
intros; elim x.
(* OZ *)
reflexivity.
(* pos n *)
simple induction n.
(* pos O *)
symmetry  in |- *; exact (add_IZ_succZ y).
(* pos (S y0) *)
intros y0 H; do 2 rewrite (tech_mult_posZ y0).
rewrite H; elim (addZ_commutativity (pos y0) (multZ (pos y0) y)).
elim (addZ_associativity (pos y0) (multZ (pos y0) y) (succZ y)).
elim (addZ_commutativity (addZ (multZ (pos y0) y) (succZ y)) (pos y0)).
rewrite (succ_addZ_r (multZ (pos y0) y) y).
rewrite (succ_addZ_l (addZ (multZ (pos y0) y) y) (pos y0)).
elim (succ_addZ_r (addZ (multZ (pos y0) y) y) (pos y0)).
reflexivity.
(* neg n *)
simple induction n.
(* neg O *)
simpl in |- *; rewrite (add_mIZ_predZ (oppZ y)); exact (opp_succZ y).
(* neg (S y0) *)
intros y0 H; do 2 rewrite (tech_mult_negZ y0).
elim H; elim (addZ_commutativity (oppZ y) (multZ (neg y0) y)).
elim (addZ_associativity (oppZ y) (multZ (neg y0) y) (neg (S y0))).
elim (addZ_commutativity (addZ (multZ (neg y0) y) (neg (S y0))) (oppZ y)).
rewrite (opp_succZ y).
rewrite (pred_addZ_r (multZ (neg y0) (succZ y)) (oppZ y)).
rewrite H; elim (pred_addZ_l (addZ (multZ (neg y0) y) (neg y0)) (oppZ y)).
elim (pred_addZ_r (multZ (neg y0) y) (neg y0)); unfold predZ in |- *;
reflexivity.
Qed.
intros; elim x.
(* OZ *)
reflexivity.
(* pos n *)
simple induction n.
(* pos O *)
simpl in |- *; symmetry  in |- *; exact (add_mIZ_predZ y).
(* pos (S n0) *)
intros n0 H; unfold oppZ in |- *; do 2 rewrite (tech_mult_posZ n0).
rewrite (pred_addZ_r (multZ (pos n0) (predZ y)) y).
elim (pred_addZ_l (multZ (pos n0) (predZ y)) y).
elim (addZ_commutativity y (multZ (pos n0) y)).
elim (addZ_associativity y (multZ (pos n0) y) (neg (S n0))).
elim (addZ_commutativity (addZ (multZ (pos n0) y) (neg (S n0))) y).
rewrite H; elim (pred_addZ_r (multZ (pos n0) y) (oppZ (pos n0))).
reflexivity.
(* neg n *)
simple induction n.
(* neg O *)
simpl in |- *.
replace (pos 0) with IZ; auto.
rewrite (add_IZ_succZ (oppZ y)).
exact (opp_predZ y).
(* neg (S n0) *)
intros n0 H; do 2 rewrite (tech_mult_negZ n0).
rewrite H; rewrite (opp_predZ y).
elim (addZ_commutativity (oppZ (neg n0)) (multZ (neg n0) y)).
elim (addZ_associativity (oppZ (neg n0)) (multZ (neg n0) y) (succZ (oppZ y))).
elim
(addZ_commutativity (addZ (multZ (neg n0) y) (succZ (oppZ y)))
(oppZ (neg n0))).
rewrite (succ_addZ_r (multZ (neg n0) y) (oppZ y)).
rewrite (succ_addZ_l (addZ (multZ (neg n0) y) (oppZ y)) (oppZ (neg n0))).
elim (succ_addZ_r (addZ (multZ (neg n0) y) (oppZ y)) (oppZ (neg n0))).
reflexivity.
Qed.
simple destruct x.
(* OZ *)
reflexivity.
(* pos n *)
simple induction n.
(* pos O *)
reflexivity.
(* pos (S y) *)
intros y H; rewrite (tech_mult_posZ y OZ); rewrite H; reflexivity.
(* neg n *)
simple induction n.
(* neg O *)
reflexivity.
(* neg (S y) *)
intros y H; rewrite (tech_mult_negZ y OZ); rewrite H; reflexivity.
Qed.
simple destruct x.
(* OZ *)
reflexivity.
(* pos n *)
simple induction n.
(* pos O *)
reflexivity.
(* pos (S y) *)
intros y H; rewrite (tech_mult_posZ y IZ); rewrite H.
rewrite (add_IZ_succZ (pos y)); reflexivity.
(* neg n *)
simple induction n.
(* neg O *)
reflexivity.
(* neg (S y) *)
intros y H; rewrite (tech_mult_negZ y IZ); rewrite H; unfold IZ in |- *;
unfold oppZ in |- *.
rewrite (add_mIZ_predZ (neg y)); reflexivity.
Qed.
simple destruct x.
(* OZ *)
reflexivity.
(* pos n *)
simple induction n.
(* pos O *)
reflexivity.
(* pos (S y) *)
intros y H; rewrite (tech_mult_posZ y (neg 0)); rewrite H.
rewrite (add_mIZ_predZ (oppZ (pos y))); reflexivity.
(* neg n *)
simple induction n.
(* neg O *)
reflexivity.
(* neg (S y) *)
intros y H; rewrite (tech_mult_negZ y (neg 0)); rewrite H.
elim
(opp_add Z IdZ addZ OZ oppZ Z_group addZ_commutativity (neg y) (neg 0) I I).
rewrite (add_mIZ_predZ (neg y)); reflexivity.
Qed.
unfold commutativity in |- *; intros; elim x.
(* OZ *)
rewrite (mult_OZ y); unfold multZ in |- *; reflexivity.
(* pos n *)
simple induction n.
(* pos O *)
simpl in |- *; symmetry  in |- *; exact (mult_IZ y).
(* pos (S y0) *)
intros y0 H; rewrite (tech_mult_posZ y0 y); rewrite H.
elim (mult_succZ_r y (pos y0)); unfold succZ in |- *; reflexivity.
(* neg n *)
intros; elim n.
(* neg O *)
simpl in |- *; symmetry  in |- *; exact (mult_mIZ y).
(* neg (S y0) *)
intros y0 H; rewrite (tech_mult_negZ y0 y); rewrite H.
elim (mult_predZ_r y (neg y0)); unfold predZ in |- *; reflexivity.
Qed.
unfold neutral in |- *.
split. exact I.
intros.
split.
(* -> *)
elim (multZ_commutativity IZ x); reflexivity.
(* <- *)
reflexivity.
Qed.
unfold distributivity in |- *; intros; case x.
(* OZ *)
split; reflexivity.
(* pos n *)
simple induction n.
(* pos O *)
split.
rewrite addZ_eq2; rewrite multZ_eq2.
rewrite (mult_succZ_l y z); exact (addZ_commutativity (multZ y z) z).
reflexivity.
(* pos (S y0) *)
intros y0 H.
elim H; intros; split.
rewrite addZ_eq3; rewrite multZ_eq3.
rewrite mult_succZ_l; rewrite H0.
elim (addZ_associativity (multZ (pos y0) z) (multZ y z) z).
elim (addZ_commutativity z (multZ y z)).
apply addZ_associativity.
do 3 rewrite multZ_eq3.
rewrite H1.
apply (add_add Z addZ addZ_commutativity addZ_associativity).
(* neg n *)
simple induction n.
(* neg O *)
split.
rewrite addZ_eq4; rewrite multZ_eq4; rewrite (mult_predZ_l y z).
exact (addZ_commutativity (multZ y z) (oppZ z)).
rewrite multZ_eq4.
apply (opp_add Z IdZ addZ OZ oppZ Z_group addZ_commutativity y z I I).
(* neg (S y0) *)
intros y0 H.
split.
(* -> *)
rewrite (tech_add_neg_predZ y0 y); rewrite (mult_predZ_l (addZ (neg y0) y) z).
elim H; intros. rewrite H0.
elim (addZ_associativity (multZ (neg y0) z) (multZ y z) (oppZ z)).
elim (addZ_commutativity (oppZ z) (multZ y z)).
rewrite (addZ_associativity (multZ (neg y0) z) (oppZ z) (multZ y z)).
elim (tech_mult_negZ y0 z); reflexivity.
(* <- *)
rewrite (tech_mult_negZ y0 (addZ y z)); rewrite (tech_mult_negZ y0 y).
rewrite (tech_mult_negZ y0 z); elim H; intros; rewrite H1.
elim
(add_add Z addZ addZ_commutativity addZ_associativity
(multZ (neg y0) y) (multZ (neg y0) z) (oppZ y)
(oppZ z)).
elim (opp_add Z IdZ addZ OZ oppZ Z_group addZ_commutativity y z I I).
reflexivity.
Qed.

(****************)
Lemma mult_oppZ_r : forall x y : Z, multZ x (oppZ y) = oppZ (multZ x y).