 by 6-node triangles
      <ul>
        <li>
          <a href = "square_nodes.txt">square_nodes.txt</a>
          the nodes.
        </li>
        <li>
          <a href = "square_elements.txt">square_elements.txt</a>
          the elements.
        </li>
        <li>
          <a href = "square_values.txt">square_values.txt</a>
          the values to be contoured.
        </li>
        <li>
          <a href = "square.png">square.png</a>
          the contour plot.
        </li>
      </ul>
    </p>

   