proposition: Lemma block_mx0 : forall m1 m2 n1 n2, block_mx (@null_mx m1 n1) (@null_mx m1 n2) (@null_mx m2 n1) (@null_mx m2 n2) === @null_mx (m1 + m2) (n1 + n2).
proof: Proof. by move=> m1 m2 n1 n2 i j; rewrite/block_mx/pastemx/trmx/null_mx/addmx/oppmx/scalemx; case: split; case: split; reflexivity. Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq choice fintype finfun bigops ssralg groups perm zmodp morphisms Ring RingClass bigopsClass Setoid Morphisms