Proof using.
intros n a ln1 ln2 t l H H0 H1;
case
height_pred_disj_larger_aux
with (a := a) (ln1 := ln1) (ln2 := ln2) (1 := H);
auto; case ln1; simpl in |- *;
[ intros (HH1, HH2); injection HH1; auto
| intros n0 l1; case l1; simpl in |- *; intuition; try discriminate ].
Qed.

(* Specifications: *)
Lemma height_pred_disj_larger2_aux :
forall (n : nat) (ln : list nat) (t : btree A) (l : list (btree A)),
height_pred n ln l t ->
forall ln1 ln2 a,
ln = ln1 ++ a :: ln2 ->
(exists n1 : _, In n1 ln1 /\ a <= n1) \/
(exists n1 : _, In n1 ln2 /\ a <= n1) \/ ln = n :: nil /\ l = t :: nil.