(* Usage: rewrite (mod_diveq (-1)) by lia *)
Definition mod_diveq c a b := proj1 (mod_diveq_iff c a b).Definition diveq c a b := proj1 (diveq_iff c a b).

Lemma eq_mod_opp m x y : x mod -m = y mod -m <-> x mod m = y mod m.