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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: october 1995                                           *)
(* file: IncrDecr.v                                             *)
(* contents: definnition of an incrementer and a decrementer    *)
(* on BVs     **** TO BE COMPLETED ****                         *)
(****************************************************************)
Require Export AdderProof.
Fixpoint BV_increment (l : list bool) : BV :=
match l with
| nil => nilbv
| false :: v => true :: v
| true :: v => false :: BV_increment v
end.
Fixpoint BV_increment_carry (l : list bool) : bool :=
match l with
| nil => true
| false :: v => false
| true :: v => BV_increment_carry v
end.
Fixpoint BV_decrement (l : list bool) : BV :=
match l with
| nil => nilbv
| false :: v => true :: BV_decrement v
| true :: v => false :: v
end.
Fixpoint BV_decrement_carry (l : list bool) : bool :=
match l with
| nil => true
| false :: v => BV_decrement_carry v
| true :: v => false
end.
simple induction v. auto.
simple induction a.
simpl in |- *. intros. rewrite H; trivial.
simpl in |- *. intros. trivial.
Qed.

Lemma length_BV_decrement :
forall v : BV, lengthbv (BV_decrement v) = lengthbv v.