proposition: Lemma block_mxEul : forall i j, A (lshift m2 i) (lshift n2 j) === Aul i j.
proof: Proof. by move=> i j; rewrite /A /block_mx /trmx; rewrite -> !pastemxEl; reflexivity. Qed.
imports: ssreflect ssrbool ssrfun eqtype ssrnat seq choice fintype finfun bigops ssralg groups perm zmodp morphisms Ring RingClass bigopsClass Setoid Morphisms