  <span class="keyword">typedef</span> <span class="identifier">__unspecified_type__</span> <span class="identifier">value_type</span><span class="special">;</span>
        <span class="keyword">typedef</span> <span class="identifier">__unspecified_type__</span> <span class="identifier">difference_type</span><span class="special">;</span>
        <span class="keyword">typedef</span> <span class="identifier">__unspecified_type__</span> <span class="identifier">distance_type</span><span class="special">;</spa