The work of Fulkerson and
Gross on incidence matrices shows that the question, whether a given incidence
matrix A can be so re-arranged by rows as to bring together all the 1’s in each
separate column, can be settled if one merely knows A through the symmetrised
product ATA. Suppose it is known that such a row re-arrangement exists; it is proved
here that A can then be re-arranged in the required way if one merely knows A
through the dual symmetrised product, AAT.
Thus ATA and AAT contain respectively (i) information sufficient to decide on
the possibility or otherwise of such a re-arrangement, and (ii) information sufficient
to determine a sorting algorithm.
Implications for archaeology are briefly discussed.
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