induction k; intuition; simpl in *.
rewrite <- mult_1_r at 1.
eapply mult_le_compat.
omega.
eauto.
Qed.

Theorem expnat_exp_le :
forall n2 n4 n,
(n2 > 0 \/ n > 0) ->
n2 <= n4 ->
expnat n n2 <= expnat n n4.