induction n; intuition; simpl in *.
inversion H; clear H; subst; intuition; simpl in *.
inversion H; clear H; subst; intuition; simpl in *.
eapply IHn; intuition.
Qed.

Theorem compFold_cons :
forall (A B : Set)(eqda : EqDec A)(c : A -> B -> Comp A)(ls : list B) b (a : A),
comp_spec eq (compFold _ c a (b :: ls)) (a' <-$ c a b; compFold _ c a' ls).