Ltac mrewrite :=
   repeat first
     [ rewrite ring_add_0_l
     | rewrite <- (ring_add_comm 0)
     | rewrite ring_mul_1_l
     | rewrite ring_mul_0_l
     | rewrite ring_distr_l
     | reflexivity
     ].

Lemma ring_opp_zero : -0 == 0.