proposition: Lemma gcdsrX : gcdsr ('X : {poly R}) %= 1.
proof: Proof. move: (gcdsr_mulX 1); rewrite mul1r=> H. exact: (eqd_trans H gcdsr1). 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)