elim H0; elim H; intros.
rewrite H2; rewrite H1.
rewrite (plus_assoc (2 * q) (2 * q0) 1).
elim (mult_plus_distr_left q q0 2).
apply (odd_intro (2 * (q + q0) + 1) (q + q0)).
auto with arith.
Qed.
Hint Resolve plus_even_odd.

Lemma plus_odd_even : forall a b : nat, odd a -> even b -> odd (a + b).
intros.