 for
      three files:
      <ul>
        <li>
          <b>cc_d1_o003_x.txt</b>
        </li>
        <li>
          <b>cc_d1_o003_w.txt</b>
        </li>
        <li>
          <b>cc_d1_o003_r.txt</b>
        </li>
      </ul>
      and similarly for the second file.
    </p>

    <p>
      Once the program has computed the multidimensional product rule,
      it again writes out three files describing the product rule,
      with a common filename prefix specified by the user, which
      might be, for 