(* RCP: *)

(* Specifications: *)
Lemma orb_impls_expo:forall(m:fmap)(x y:dart),
inv_hmap m -> exd m x -> exd m y ->
impls (Iter_orb m x) (Iter_orb m y) -> expo m x y.
Lemma disjs_orb_not_expo:forall(m:fmap)(x y:dart),
inv_hmap m -> exd m x -> exd m y ->
disjs (Iter_orb m x) (Iter_orb m y) -> ~expo m x y.