proposition: Lemma block_mxElr : forall i j, A (rshift m1 i) (rshift n1 j) === Alr i j.
proof: Proof. by move=> i j; rewrite /A /block_mx /trmx; rewrite -> !pastemxEr; reflexivity. Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq choice fintype finfun bigops ssralg groups perm zmodp morphisms Ring RingClass bigopsClass Setoid Morphisms