proposition: Lemma comm_mxN f g : comm_mx f g -> comm_mx f (- g).
proof: Proof. by rewrite /comm_mx mulmxN mulNmx => ->. 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)