proposition: Lemma equivf_trans : transitive equivf.
proof: Proof. move=> [x Px] [y Py] [z Pz]; rewrite /equivf /= mulrC => /eqP xy /eqP yz. by rewrite -(inj_eq (mulfI Px)) mulrA xy -mulrA yz mulrCA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(ssrAC choice tuple bigop ssralg poly polydiv) mathcomp(generic_quotient)