intuition.
simpl.
subst.
destruct (eqd1 a2 x); destruct (eqd2 a2 x); subst; intuition.
Qed.

Theorem evalDist_seq_step :
forall (A B :Set)(c : Comp A)(f : A -> Comp B) b,
evalDist (Bind c f) b ==
sumList (getSupport c) (fun a => evalDist c a * evalDist (f a) b).