Conover, R J Beckman,<br>
          A Comparison of Three Methods for Selecting Values of Input
          Variables in the Analysis of Output From a Computer Code,<br>
          Technometrics,<br>
          Volume 21, pages 239-245, 1979.
        </li>
        <li>
          Albert Nijenhuis and Herbert Wilf,<br>
          Combinatorial Algorithms,<br>
          Academic Press, 1978, second edition,<br>
          ISBN 0-12-519260-6.
        </li>
        <li>
          Herbert Ryser,<br>
          Combinato