proposition: Lemma pastemxEl : forall A1 A2 i j, pastemx A1 A2 i (lshift n2 j) === A1 i j.
proof: Proof. by rewrite/pastemx=> A1 A2 i j; rewrite (unsplitK (inl _ _)); reflexivity. Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq choice fintype finfun bigops ssralg groups perm zmodp morphisms Ring RingClass bigopsClass Setoid Morphisms