proposition: Lemma addmx_paste : forall m n1 n2 (A1 B1 : 'M_(m, n1)) (A2 B2 : 'M_(m, n2)), pastemx A1 A2 +m pastemx B1 B2 === pastemx (A1 +m B1) (A2 +m B2).
proof: Proof. by move=> m n1 n2 iA1 B1 A2 B2 i j; rewrite/pastemx/trmx/null_mx/addmx/oppmx/scalemx; 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