proposition: Lemma fgmulC : @commutative {malg R[K]} _ *%R.
proof: Proof. move=> g1 g2; apply/malgP=> k; rewrite mcoeffMl mcoeffMr. apply/eq_bigr=> /= k1 _; apply/eq_bigr=> /= k2 _. by rewrite mulrC [X in X==k]mulmC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path choice finset fintype finfun) mathcomp(tuple bigop ssralg ssrint ssrnum) xfinmap