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

(* tests *)
Lemma tofrac0 : 0%:F = 0. Proof. exact: rmorph0. Qed.