“…The lower bound is 19 and the upper bound is 23. A lot of effort has been exerted to improve the algorithm of Laderman [27] (decomposition with rank 23), there are many algorithms with the same complexity [18], [16], [31], [23], [5], but the proof that a decomposition to a rank smaller than 23 is impossible is not known yet. For more introductory texts to the subject see, e.g., [7], [27], [8], [19].…”