span><span class=identifier>phonebook_entry</span><span class=special>::</span><span class=identifier>given_name</span><span class=special>&gt;</span>
<span class=special>&gt;</span>
</pre></blockquote>

Note that we did not even have to specify the first <code>phonebook_entry</code>
argument: the internal machinery of <code>key</code> automatically deduces it for
us. Check the <a href="../reference/key_extraction.html#key_synopsis">reference</a>
for technical details.

<h2><a name="advanced_key_extractors"