ass=special>,</span><span class=string>&quot;Dorothea&quot;</span><span class=special>));</span>
<span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span> <span class=identifier>number</span><span class=special>=</span><span class=identifier>it</span><span class=special>-&gt;</span><span class=identifier>phone_number</span><span class=special>;</span>
</pre></blockquote>

<p>
Composite keys are sorted by lexicographical order, i.e. sorting is performed
by the first k