Local Hint Resolve le_0_w lt02w le02w : a.
Local Hint Resolve le_0_p le_0_l lt_l_2w le_0_v lt_v_2w : a.

Lemma le_0_x : 0 <= x.
unfold x. fold (0 + 0). apply Zplus_le_compat; auto with a. apply Zmult_le_0_compat; auto with a. Qed.