(* fracions form a commutative ring *)
Definition frac_comRingMixin := ComRingMixin mulA mulC mul1_l mul_addl nonzero1.Canonical frac_ringType := Eval hnf in RingType type frac_comRingMixin.Canonical frac_comRingType := Eval hnf in ComRingType type mulC.

Lemma inv0 : inv 0%:F = 0%:F.