proposition: Lemma block_mxKur : ursubmx A = Aur.
proof: Proof. by rewrite /ursubmx col_mxKu row_mxKr. 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)