induction 1; intuition.
unfold compFold.
eapply evalDist_ret_eq.
intuition.
unfold compFold.
comp_skip.
Qed.

Lemma list_pred_flatten_both :
forall (A B : Set)(P : A -> B -> Prop)(lsa : list (list A))(lsb : list (list B)),
list_pred (list_pred P) lsa lsb ->
list_pred P (flatten lsa) (flatten lsb).