Canonical dvdz_oppPred d := OpprPred (dvdz_zmod_closed d).
Canonical dvdz_zmodPred d := ZmodPred (dvdz_zmod_closed d).

(* Greatest common divisor *)
Lemma gcdzz m : gcdz m m = `|m|%:Z. Proof. by rewrite /gcdz gcdnn. Qed.