instance, <i>product</i>, in which case the files
      would be:
      <ul>
        <li>
          <b>product_x.txt</b>
        </li>
        <li>
          <b>product_w.txt</b>
        </li>
        <li>
          <b>product_r.txt</b>
        </li>
      </ul>
    </p>

    <p>
      For information on the form of these files, see the
      <b>QUADRATURE_RULES</b> directory listed below.
    </p>

    <h3 align = "center">
      Usage:
    </h3>

    <p>
      <blockquote>
        <b>product_rule</b> ( <i