Qed.

(* Specifications: *)
Lemma minus_le_lem2c : forall a b : nat, a - S b <= a - b.
intros. pattern a, b in |- *. apply nat_double_ind. auto with arith.
Lemma true_to_false : true = negb false.
auto.
Lemma IsNull_false :
forall (a : bool) (v : BV), IsNull (consbv a v) = true -> a = false.