proposition: Lemma scalemxA : forall x y A, x *m: (y *m: A) === (x * y) *m: A.
proof: Proof. by rewrite/null_mx/addmx/oppmx/scalemx=> x y 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