Notation NoDup := (NoDupA E.eq).Notation InA := (InA E.eq).

Theorem fold_rec_bis : forall (A:Type)(P : t -> A -> Type)(f : elt -> A -> A)(i:A)(s:t), (forall s s' a, s[=]s' -> P s a -> P s' a) -> (P empty i) -> (forall x a s', In x s -> ~In x s' -> P s' a -> P (add x s') (f x a)) -> P s (fold f s i).