    The Turing Omnibus,<br>
          Freeman, 1989,<br>
          ISBN13: 9780716781547,<br>
          LC: QA76.D45.
        </li>
        <li>
          Brian Hayes,<br>
          The Easiest Hard Problem,<br>
          American Scientist,<br>
          Volume 90, Number 2, March-April 2002, pages 113-117.
        </li>
        <li>
          Silvano Martello, Paolo Toth,<br>
          Knapsack Problems: Algorithms and Computer Implementations,<br>
          Wiley, 1990,<br>
          ISBN: 0-471-92420-2,