proposition: Lemma trmx_ursub : (ursubmx A)^T === llsubmx A^T.
proof: Proof. by move => i j /=; reflexivity. Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq choice fintype finfun bigops ssralg groups perm zmodp morphisms Ring RingClass bigopsClass Setoid Morphisms