t;());</span>
<span class="special">}</span>
</pre>
<p>
        </p>
<p>
          The <code class="computeroutput"><span class="identifier">on_custom_relation</span></code>
          method is called with the relation name (the "is_in_rectangle"
          string in our case) and the right-hand argument for the relation (the rectangle
          description). All we have to do is to construct the filter, which is implemented
          by our <code class="computeroutput"><span class="identifier">is_in_rectang