proposition: Lemma unitmxZ a A : a \is a GRing.unit -> (a *: A \in unitmx) = (A \in unitmx).
proof: Proof. by move=> Ua; rewrite !unitmxE detZ unitrM unitrX. 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)