intros l H; generalize (permutation_length _ _ H); case l; simpl in |- *;
auto.
intros; discriminate.
Qed.

(* Specifications: *)
Lemma permutation_one_inv_aux :
forall l1 l2 : list A,
permutation l1 l2 -> forall a : A, l1 = a :: nil -> l2 = a :: nil.