Definition ulsubmx := lsubmx (usubmx A).Definition ursubmx := rsubmx (usubmx A).Definition dlsubmx := lsubmx (dsubmx A).Definition drsubmx := rsubmx (dsubmx A).

Lemma block_mxEur i j : A (lshift m2 i) (rshift n1 j) = Aur i j.