proposition: Lemma scale1mx : forall A, 1 *m: A === A.
proof: Proof. by rewrite/null_mx/addmx/oppmx/scalemx=> A i j; ring. Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq choice fintype finfun bigops ssralg groups perm zmodp morphisms Ring RingClass bigopsClass Setoid Morphisms