code> and <code>C2</code> must be of the same class.</p>
    </div>

    <div id="ref-examples">
    <h2>Examples</h2>
    <div class="sourceCode"><pre class="sourceCode r"><code><span class="r-in"><span><span class="co"># Build two sparse sets</span></span></span>
<span class="r-in"><span><span class="va">S</span> <span class="op">&lt;-</span> <span class="va"><a href="Set.html">Set</a></span><span class="op">$</span><span class="fu">new</span><span class="op">(</span>attributes <span class="op">=</span> <