crisply distinguished from the
others.  <a class="reference external" href="../../../python/doc/index.html">Boost.Python</a> does this by requiring that <tt class="docutils literal">base_list</tt> be
a specialization of its <tt class="docutils literal">bases&lt; … &gt;</tt> template (as opposed to
being any old MPL sequence) and by requiring that <tt class="docutils literal">copyable</tt>, if
explicitly supplied, be <tt class="docutils literal"><span class="pre">boost::noncopyable</span></tt>.  One easy w