(* we show that equivf is an equivalence *)
Definition type := {eq_quot equivf}.
Definition type_of of phant R := type.
Notation "{ 'fraction' T }" := (type_of (Phant T)).
(* we recover some structure for the quotient *)
Canonical frac_quotType := [quotType of type].
Canonical frac_eqType := [eqType of type].
Canonical frac_choiceType := [choiceType of type].
Canonical frac_eqQuotType := [eqQuotType equivf of type].
Canonical frac_of_quotType := [quotType of {fraction R}].
Canonical frac_of_eqType := [eqType of {fraction R}].
Canonical frac_of_choiceType := [choiceType of {fraction R}].
Canonical frac_of_eqQuotType := [eqQuotType equivf of {fraction R}].

(* we explain what was the equivalence on the quotient *)
Lemma equivf_def (x y : ratio R) : x == y %[mod type]
= (\n_x * \d_y == \d_x * \n_y).