(* UNICITY OF THE INDICE mod p: *)

Lemma unicity_mod_p:forall(m:fmap)(z:dart)(j k:nat),
inv_hmap m -> exd m z ->
let p := Iter_upb m z in
(j < p)%nat -> (k < p)%nat ->
Iter (f m) j z = Iter (f m) k z -> j = k.