intuition.
eapply refl.
eapply evalDist_left_ident_eq.
Qed.

Theorem evalDist_assoc :
forall rel (A : Set)(c1 : Comp A)(B C : Set)(c2 : A -> Comp B)(c3 : B -> Comp C) x,
RatRel rel ->
rel (evalDist (Bind (Bind c1 c2) c3) x) (evalDist (Bind c1 (fun a => (Bind (c2 a) c3))) x).