proposition: Lemma comm_mxP f g : reflect (comm_mx f g) (comm_mxb f g).
proof: Proof. exact: eqP. 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)