proposition: Lemma mulr_gcdsl : forall a p, gcdsr p * a %= gcdsr (p * a %:P).
proof: Proof. by move=> a p; rewrite eqd_sym gcdsr_mulr. 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)