proposition: Lemma pi_mul : {morph \pi : x y / mulf x y >-> mul x y}.
proof: Proof. move=> x y; unlock mul; apply/eqmodP=> /=. rewrite equivfE /= /addf /= !numden_Ratio ?mulf_neq0 ?domP //. by rewrite mulrACA !equivf_r mulrACA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(ssrAC choice tuple bigop ssralg poly polydiv) mathcomp(generic_quotient)