(* Copyright (C) 2005-2008 Sebastien Briais *)
(* http://lamp.epfl.ch/~sbriais/ *)
(* This library is free software; you can redistribute it and/or modify *)
(* it under the terms of the GNU Lesser General Public License as *)
(* published by the Free Software Foundation; either version 2.1 of the *)
(* License, or (at your option) any later version. *)
(* This library is distributed in the hope that it will be useful, but *)
(* WITHOUT ANY WARRANTY; without even the implied warranty of *)
(* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU *)
(* Lesser General Public License for more details. *)
(* You should have received a copy of the GNU Lesser General Public *)
(* License along with this library; if not, write to the Free Software *)
(* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA *)
(* 02110-1301 USA *)
Require Export Arith.
Require Export ArithRing.
Require Export Omega.
Unset Standard Proposition Elimination Names.
intros.
rewrite mult_comm.
induction m;simpl;auto with arith.
elim H0;trivial.
Qed.
intros.
induction n.
tauto.
simpl in H.
right.
assert (m <= O);try omega.
rewrite <- H.
auto with arith.
Qed.
intros.
rewrite mult_comm.
induction m.
inversion H0.
simpl.
assert (O < m*n);try omega.
inversion H0;try omega.
assert (1 <= n);try omega.
assert (m > 1);try omega.
generalize (IHm H4);omega.
Qed.
intros n m.
case n.
left;trivial.
intros.
right.
destruct m.
rewrite mult_comm in H.
discriminate.
destruct m;trivial.
assert ((S n0)<(S n0)*(S (S m))).
apply mult_lemma3;intros;auto with arith.
rewrite <- H in H0.
elim (lt_irrefl (S n0) H0).
Qed.
induction n;simpl;intros;try discriminate.
induction m.
rewrite mult_comm in H.
simpl in H;discriminate.
assert ((S n)<=((S n)*(S m))).
apply mult_lemma1;discriminate.
assert (((S n)*(S m))=((S m)+n*(S m))).
reflexivity.
rewrite H1 in H0.
rewrite H in H0.
assert ((S n)=1).
omega.
split;trivial.
inversion H2.
rewrite H4 in H.
simpl in H.
omega.
Qed.
induction y;intros;rewrite plus_comm;simpl.
auto with arith.
rewrite plus_comm.
apply IHy.
Qed.
intros.
induction a.
simpl.
trivial.
replace (S a*n) with (n+a*n);try (auto with arith).
rewrite plus_comm.
rewrite plus_minus_lemma1.
simpl.
rewrite <- minus_n_O;trivial.
Qed.
induction a.
intros;rewrite <- mult_n_O in H0; generalize (mult_lemma2 n b); intros Hl2; elim Hl2; intros; (auto || elim H ; auto).
intros b n H.
rewrite mult_comm;simpl;rewrite mult_comm;intro.
assert (n*a = n*b-n).
apply plus_minus;auto.
assert (a*n=(b-1)*n).
rewrite <- mult_minus_lemma1;rewrite mult_comm;rewrite (mult_comm b n);trivial.
assert (a=(b-1)).
apply (IHa (b-1) n);trivial.
rewrite mult_comm;rewrite (mult_comm n (b-1));trivial.
destruct b;simpl in H3.
rewrite H3 in H0;rewrite (mult_comm n 0) in H0;rewrite plus_comm in H0;simpl in H0;elim H;trivial.
rewrite <- minus_n_O in H3;auto.
Qed.

Lemma mult_lemma7 : forall (x y z t:nat),x*y*(z*t)=z*(x*y*t).