ion function</strong></span></em></span>, because it allows to select parts
          of a maps using <span class="emphasis"><em>key</em></span> or <span class="emphasis"><em>selection objects</em></span>.
          So we have a <span class="emphasis"><em><span class="bold"><strong>generalized intersection</strong></span></em></span>
          for these overloads,
        </p>
<p>
          
</p>
<pre class="programlisting"><span class="comment">/* (Generalized) intersection */</span>   <span class="special