proposition: Lemma tofrac_is_multiplicative: multiplicative tofrac.
proof: Proof. split=> [p q|//]; unlock tofrac; rewrite -[RHS]pi_mul. by rewrite /mulf /= !numden_Ratio ?(oner_neq0, mul1r, mulr1). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(ssrAC choice tuple bigop ssralg poly polydiv) mathcomp(generic_quotient)