proposition: Lemma pastemxEr : forall A1 A2 i j, pastemx A1 A2 i (rshift n1 j) === A2 i j.
proof: Proof. by rewrite/pastemx=> A1 A2 i j; rewrite (unsplitK (inr _ _)); reflexivity. Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq choice fintype finfun bigops ssralg groups perm zmodp morphisms Ring RingClass bigopsClass Setoid Morphisms