Proof (eqmod_small_eq modulus).
Hint Resolve eqm_small_eq: ints.

(* Specifications: *)
Lemma eqm_add:
forall a b c d, eqm a b -> eqm c d -> eqm (a + c) (b + d).
Lemma eqm_add:
forall a b c d, eqm a b -> eqm c d -> eqm (a + c) (b + d).