(** Specification of [map2] *)

(* Specifications: *)
Lemma map2_1 :
forall m (Hm : sort (@ltk elt) m) m' (Hm' : sort (@ltk elt') m')(x:key),
In x m \/ In x m' ->
find x (map2 m m') = f (find x m) (find x m').
Lemma map2_2 :
forall m (Hm : sort (@ltk elt) m) m' (Hm' : sort (@ltk elt') m')(x:key),
In x (map2 m m') -> In x m \/ In x m'.