proposition: Lemma block_mxKul : ulsubmx A === Aul.
proof: Proof. by move=> i j; rewrite /A /block_mx /ulsubmx /lcutmx /trmx; rewrite -> !pastemxEl; reflexivity. Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq choice fintype finfun bigops ssralg groups perm zmodp morphisms Ring RingClass bigopsClass Setoid Morphisms