an class="keyword">typedef</span></code> <span class="emphasis"><em>see
            below</em></span> <code class="computeroutput"><span class="identifier">difference_type</span><span class="special">;</span></code></span></dt>
<dd><p>
                <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">difference_type</span></code> if such a type
                exists; otherwise <code class="computeroutput"><span class="identifier">std</span