intros; cut ({n < m /\ m < p} + {p <= m /\ m < t}).
intro; elim H0; intro y.
left; apply (inser_trans_lt n m p q y).
right; auto with core arith.
apply (inser_trans_lt n m t p H).
Qed.

(**********)
Lemma eq_le : forall n m : nat, n = m -> n <= m.
intros; omega.