<span class="identifier">ref</span><span class="special">(</span><span class="identifier">a</span><sub><span class="number">1</span></sub><span class="special">)</span><span class="special">,</span> &#8230; <span class="identifier">boost</span><span class="special">::</span><span class="identifier">ref</span><span class="special">(</span><span class="identifier">a</span><sub><span class="identifier">N</span><span class="special">-</span><span class="number">1</span></sub><span class="special">)</span></pre>