::valid_member_type</a></code>
              </p>
              <p>
                class T = a type
              </p>
              <p>
                class U = (optional) marker type
              </p>
              <p>
                returns = true if the type exists, false if it does not. 'Existence'
                is determined by whether the type does not equal the marker type
                of BOOST_TTI_MEMBER_TYPE.
              </p>
            </td>
<td>
              <p>
                <cod