Canonical dvdC_opprPred x := OpprPred (dvdC_zmod x).
Canonical dvdC_addrPred x := AddrPred (dvdC_zmod x).
Canonical dvdC_zmodPred x := ZmodPred (dvdC_zmod x).

(* Elementary modular arithmetic. *)
Lemma eqCmod_refl e x : (x == x %[mod e])%C.