intuition.
eapply (@expected_poly_time_compose_0 _ _ _ _ _ (fun n b => f3 n (f1 n) b)); eauto.
eapply (@expected_poly_time_compose_0 _ _ _ _ _ (fun n b => f3 n b)); eauto.
Qed.

Theorem expected_poly_time_bind_0_f :
forall (A B : nat -> Set) (a : forall n, Comp (A n)) (b : forall n, A n -> Comp (B n)),
efficient _ a ->
efficient _ b ->
efficient _ (fun n => (Bind (a n) (b n))).