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(* GNU General Public License for more details.                       *)
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(* 02110-1301 USA                                                     *)
(** This file includes random facts about Integers (and natural numbers) which are not found in the standard library. Some of the lemma here are not used in the QArith developement but are rather useful. *)
Require Export ZArith.
Require Export ZArithRing.
Tactic Notation "ElimCompare" constr(c) constr(d) := elim_compare c d.
Ltac Flip :=
apply Z.gt_lt || apply Z.lt_gt || apply Z.le_ge || apply Z.ge_le; assumption.
Ltac Falsum :=
try intro; apply False_ind;
repeat
match goal with
| id1:(~ ?X1) |- ?X2 =>
(apply id1; assumption || reflexivity) || clear id1
end.
Ltac Step_l a :=
match goal with
|  |- (?X1 < ?X2)%Z => replace X1 with a; [ idtac | try ring ]
end.
Ltac Step_r a :=
match goal with
|  |- (?X1 < ?X2)%Z => replace X2 with a; [ idtac | try ring ]
end.
Ltac CaseEq formula :=
generalize (refl_equal formula); pattern formula at -1 in |- *;
case formula.

Lemma pair_2 :
forall (A B : Set) (H1 H2 : A * B),
fst H1 = fst H2 -> snd H1 = snd H2 -> H1 = H2.