proposition: Lemma rmorph_comm (S : ringType) (f : {rmorphism R -> S}) x y : comm (f x) (f y).
proof: Proof. by red; rewrite -!rmorphM mulrC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)