span class="bold"><strong>Aliases:</strong></span> <code class="computeroutput"><span class="identifier">Op</span><span class="special">&lt;</span><span class="identifier">Args</span><span class="special">...&gt;</span></code> if it is a valid template-id, otherwise
        <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">nonesuch</span></code>.
      </p>
<p>
        <span class="bold"><strong>C++ Standard Paper:</strong></span> <a hr