proposition: Lemma mulr_gcdsr : forall a p, a * gcdsr p %= gcdsr (a%:P * p).
proof: Proof. by move=> a p; rewrite eqd_sym gcdsr_mull. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(path choice fintype tuple finset ssralg) mathcomp(matrix poly) mathcomp(bigop polydiv) CoqEAL(stronglydiscrete dvdring)