Proof using.
intros a l1; generalize a; elim l1; simpl in |- *; auto; clear a l1.
intros a l H a0 l2; rewrite H; auto.
Qed.

Theorem fold_left_init :
(forall (a : A) (b : B), h (f a b) = f (h a) b) ->
forall (a : A) (l : list B), fold_left f l (h a) = h (fold_left f l a).