intros a0 l0 H' H'0.
case (in_app_or _ _ _ H'0); simpl in |- *; intros H'1; auto.
elim H'1; auto.
intros H'2; elim H'2.
Qed.

Lemma in_rev : forall (A : Set) (a : A) (l : list A), In a l -> In a (rev l).
intros A a l H'.