Definition R2
 (m:fmap)(z:dart)(s:set):Prop:=
   let sr := Iter_rem_aux m z s in
    ~ exds sr (Iter (f m) (ndN m - card s)%nat z).

(* Specifications: *)
Lemma LR2 : forall(m:fmap)(z:dart)(s:set), let sr := Iter_rem_aux m z s in ~ exds sr (Iter (f m) (ndN m - card s)%nat z).