proposition: Lemma mulrC : @commutative U U *%R.
proof: Proof. by move=> x y; apply: val_inj; rewrite !rmorphM mulrC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)