(* THE upb_ITERATED DART BY f IS IN THE COMPLEMENTARY: *)

(* Specifications: *)
Lemma exd_Iter_orb_upb :
forall(m:fmap)(z:dart),
inv_hmap m -> exd m z ->
let n:= Iter_upb m z in
exds (Iter_orb m z) (Iter (f m) n z).