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(* 02110-1301 USA                                                     *)
(* Contribution to the Coq Library   V6.3 (July 1999)                    *)
(****************************************************************)
(*           The Calculus of Inductive Constructions            *)
(*                       COQ v5.10                              *)
(*                                                              *)
(* Laurent Arditi.  Laboratoire I3S. CNRS ura 1376.             *)
(* Universite de Nice - Sophia Antipolis                        *)
(* arditi@unice.fr, http://wwwi3s.unice.fr/~arditi/lolo.html    *)
(*                                                              *)
(* date: may 1995                                               *)
(* file: Bool_compl.v                                           *)
(* contents: additional lemmas about bool, definition of xor,   *)
(* bool_to_nat and if_then_else                                 *)
(****************************************************************)
Require Export Bool.
simple induction a; simple induction b; auto.
Qed. Hint Resolve neg_eq.
auto.
Qed.
auto.
Qed.
Definition xorb (b1 b2 : bool) : bool := b1 && negb b2 || negb b1 && b2.
simple induction b; auto.
Qed. Hint Resolve xorb_b_b.
simple induction b; auto.
Qed. Hint Resolve xorb_b_false.
simple induction b; auto.
Qed. Hint Resolve xorb_b_true.
(****************************************************************)
Definition bool_to_nat (b : bool) :=
match b with
| true => 1
| false => 0
end.
simple induction b; auto.
Qed. Hint Resolve bool_to_nat_all.
(* Lemma bool_to_nat_negb : (b:bool) (bool_to_nat (negb b))=(minus (S O) (bool_to_nat b)). Induction b;Auto. Qed. Hints Resolve bool_to_nat_negb. *)
(****************************************************************)
(* Conditionnelle polymorphique: le test est un booleen,        *)
(* les clauses d'un type quelconque (le meme pour les 2 clauses *)
Definition If (T : Set) (b : bool) (x y : T) :=
match b with
| true => x
| false => y
end.
simple induction b; simpl in |- *; trivial.
Qed. Hint Resolve If_neg.
simple induction b; simpl in |- *; trivial.
Qed. Hint Resolve If_eq.
simple induction b2; auto.
Qed.

Lemma If_cond_true :
forall (T : Set) (a : bool) (x y : T), x <> y -> If T a x y = x -> a = true.