induction n; destruct ls; intuition; simpl in *.
f_equal.
eapply  listReplace_twice_nil.
f_equal.
eauto.
Qed.

Lemma compFold_foldBodyOption_None :
forall (A B : Set)(eqd : EqDec A)(c : A -> B -> Comp (option A))(ls : list B) x,
evalDist (compFold _ (foldBody_option _ c) None ls) x ==
evalDist (ret None) x.