tor w(x):
      <ul>
        <li>
          <b>option</b> = 0, the unweighted integral:
          <pre>
            Integral ( -oo &lt; x &lt; +oo ) f(x) dx
          </pre>
        </li>
        <li>
          <b>option</b> = 1, the physicist weighted integral:
          <pre>
            Integral ( -oo &lt; x &lt; +oo ) exp(-x*x) f(x) dx
          </pre>
        <li>
          <b>option</b> = 2, the probabilist weighted integral:
          <pre>
            Integral ( -oo &lt; x &lt; +oo ) exp(-x*x/2) f(x