Definition corable {A} {JA: Join A}{PA: Perm_alg A}{SA: Sep_alg A}
         (P: pred A) := forall w, P w = P (core w).

Lemma corable_exp {A} {JA: Join A}{PA: Perm_alg A}{SA: Sep_alg A}: forall {B: Type} (P: B -> pred A) , (forall b, corable (P b)) -> corable (exp P).