intros a l i below_l.
unfold below_list in |- *.
intros b in_b.
apply below_l.
right; assumption.
Qed.

(* Specifications: *)
Lemma below_cons_list :
forall (a : form) (l : flist) (i : Int),
below_form a i -> below_list l i -> below_list (a :: l) i.