        objects</em></span> which are <span class="emphasis"><em>key elements, intervals</em></span>
          and <span class="emphasis"><em>Sets of keys</em></span>.
        </p>
<p>
          
</p>
<pre class="programlisting"><span class="comment">// overload tables for             element containers:     interval containers:
</span><span class="identifier">T</span><span class="special">&amp;</span> <span class="keyword">operator</span> <span class="special">&amp;=</span> <span class="special">(</span><s