intuition.
eapply constant_cost_le.
eapply (constant_cost_compose f2 (fun _ x => f3 b x)).
eauto.
eapply constant_cost_const.
intuition.
eauto.
omega.
Qed.

Theorem constant_cost_bind_const1 :
forall (A  : Type)(B C: Set)
(f1 : Comp B)(f2 : A -> B -> Comp C) c1 c2,
cost f2 c1 ->
(forall a, cost (f2 a) c2) ->
cost (fun a => Bind f1 (f2 a)) (c1 + c2).