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

Lemma block_mxEh : block_mx Aul Aur Adl Adr = row_mx (col_mx Aul Adl) (col_mx Aur Adr).