difference_type</span><span class="special">;</span>

<span class="keyword">private</span><span class="special">:</span>
    <span class="keyword">friend</span> <span class="keyword">class</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">iterator_core_access</span><span class="special">;</span>

    <span class="keyword">void</span> <span class="identifier">increment</span><span class="special">()</span>
    <span class="special">{</span>
        <span clas