Definition Q2(m:fmap)(z:dart)(s:set):Prop:=
  exds s (Iter (f m) (ndN m - card s)%nat z) ->
      (card (Iter_rem_aux m z s) < card s)%nat.

(* Specifications: *)
Lemma LQ2:forall(m:fmap)(z:dart)(s:set), exds s (Iter (f m) (ndN m - card s) z) -> (card (Iter_rem_aux m z s) < card s)%nat.