(* fractions form a ring with explicit unit *)
Canonical frac_unitRingType := Eval hnf in UnitRingType type RatFieldUnitMixin.
Canonical frac_comUnitRingType := [comUnitRingType of type].

Lemma tofracMn n : {morph tofrac: x / x *+ n}. Proof. exact: rmorphMn. Qed.