f1 f2 (p : fraction_eq f1 f2) : fraction_eq (frac_negate f1) (frac_negate f2). Proof. destruct p as [x [s p]]. refine (x; (s,_)); simpl. rewrite 2 rng_mult_negate_r, 2 rng_mult_negate_l. f_ap. Defined.
Require Import Basics.Overture Basics.Trunc Basics.Tactics Colimits.Quotient