proposition: Lemma comm_mx_scalar n a (A : 'M[R]_n) : comm_mx A a%:M.
proof: Proof. exact: scalar_mxC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype finfun bigop finset fingroup perm order) mathcomp(div prime binomial ssralg countalg finalg zmodp)