Empty set representation
<p>Could someone explain the following?</p>

<pre><code>&gt;&gt;&gt; a = {1}
&gt;&gt;&gt; b = {2}
&gt;&gt;&gt; a &amp; b == set()
True
&gt;&gt;&gt; a &amp; b == {}
False
</code></pre>

<p>Why is this choice made?</p>
