K-1, where K is an integer, so that at each level of the hierarchy there are 4i sub-blocks of size M/2i ???M/2i, and starting with the K-1 in the hierarchy and proceeding to successive levels in the hierarchy, testing each set of four childless brother/sister sub-blocks and merging each set of four childless brother/sister sub-blocks and merging each set of four childless brother/sister sub-blocks