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