Definition R3
(m:fmap)(z t:dart)(s:set):Prop:=
~ exds s t ->
let sr := Iter_rem_aux m z s in
~ exds sr t.

(* Specifications: *)
Lemma LR3:forall(m:fmap)(z t:dart)(s:set),
~ exds s t ->
let sr := Iter_rem_aux m z s in
~ exds sr t.