se [ 0, 2^N-1].
          This argument is optional, and if omitted, the full range is searched.
        </li>
        <li>
          <i>c</i>, a vector containing the indices of the weights used to
          make the combination.  This array is empty if no solution was found.
          Otherwise, the list of weights used to form the sum is <i>w(c)</i>.
        </li>
        <li>
          <i>index</i>, the index, between <i>r(1)</i> and <i>r(2)</i>, of the solution
          that was found, or an empty val