Definition invf x : dom := Ratio \d_x \n_x.
Definition inv := lift_op1 {fraction R} invf.

(* Specifications: *)
Lemma pi_inv : {morph \pi : x / invf x >-> inv x}.
Canonical pi_inv_morph := PiMorph1 pi_inv.
Lemma addA : associative add.
Lemma addC : commutative add.
Lemma add0_l : left_id 0%:F add.
Lemma addN_l : left_inverse 0%:F opp add.
Definition frac_zmodMixin :=  ZmodMixin addA addC add0_l addN_l.