proposition: Lemma mxOverZ (S : mulrClosed R) : {in S & mxOver S, forall a : R, forall v : 'M[R]_(m, n), a *: v \is a mxOver S}.
proof: Proof. by move=> a v aS /mxOverP vS; apply/mxOverP => i j; rewrite !mxE rpredM. 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)