ubsets should be checked.  On the other hand, this full
      range could be broken down into smaller subranges, each of
      which could be checked independently.
    </p>

    <p>
      It is possible that, in the given range, there may be multiple
      solutions of the problem.  This function will only return
      one such solution, if found.  However, the function may be called
      again, with an appropriate restriction of the range, to continue
      the search for other solutions.
    </p>

    <