Proof using.
intros l t1 t2 t3 H; generalize t2 t3; elim H; clear H l t1 t2 t3;
auto with datatypes.
simpl in |- *; intros t t2 t3 [H1| H1]; auto.
rewrite H1; auto.
case H1.
intros l1 l2 t1 t2 t3 H H0 H1 t0 t4 H2 H3.
cut (In t0 (t1 :: t2 :: l2)); auto.
simpl in |- *; intros [H4| [H4| H4]]; auto with datatypes.
apply (H1 (node t1 t2)); simpl in |- *; auto.
rewrite H4; auto.
apply (H1 (node t1 t2)); simpl in |- *; auto.
rewrite H4; auto.
apply (H1 t0); simpl in |- *; auto.
apply permutation_in with (1 := H); simpl in |- *; auto.
Qed.

(* Specifications: *)
(* Trees of the cover are subtrees of the tree *)
Theorem cover_in_inb : forall l t1 t2, cover l t1 -> In t2 l -> inb t2 t1.
Proof using.