Proof using.
intros t1 t2 H; elim H; clear H t1 t2; simpl in |- *; auto.
intros t t1 t2 H H0; apply le_trans with (1 := H0); auto with arith.
intros t t1 t2 H H0; apply le_trans with (1 := H0); auto with arith.
Qed.

(* Belonging is anisymmetric *)
Theorem inb_antisym : forall t1 t2 : btree, inb t1 t2 -> inb t2 t1 -> t1 = t2.
Proof using.