proposition: Lemma dvdC_mul2r x y z : y != 0 -> (x * y %| z * y)%C = (x %| z)%C.
proof: Proof. move=> nz_y; rewrite !unfold_in !(mulIr_eq0 _ (mulIf nz_y)). by rewrite mulrAC invfM mulrA divfK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun ssrnat eqtype seq choice) mathcomp(div fintype path bigop finset prime order ssralg) mathcomp(poly polydiv mxpoly generic_quotient countalg) mathcomp(ssrnum closed_field ssrint archimedean rat intdiv) mathcomp(algebraics_fundamentals)