(** Specification of [equal] *)

(* Specifications: *)
Lemma equal_1 : forall m (Hm:NoDupA m) m' (Hm': NoDupA m') cmp,
Equivb cmp m m' -> equal cmp m m' = true.
Lemma equal_2 : forall m (Hm:NoDupA m) m' (Hm':NoDupA m') cmp,
equal cmp m m' = true -> Equivb cmp m m'.