>abstract</span><span class="special">&gt;();</span>

<span class="comment">// Contrary to the two key types, the information will be mutable</span>
<span class="comment">// using iterators.</span>

<span class="identifier">i</span><span class="special">-&gt;</span><span class="identifier">get</span><span class="special">&lt;</span><span class="identifier">abstract</span><span class="special">&gt;()</span> <span class="special">+=</span> <span class="string">"More details about this book"</span><span class=