irst</span><span class="o">.</span><span class="n">pred</span> <span
            class="o">=</span> <span class="n">last</span>
    <span class="n">T</span><span class="o">.</span><span class="n">last</span> <span class="o">=</span> <span
            class="n">last</span>
    <span class="n">T</span><span class="o">.</span><span class="n">last</span><span class="o">.</span><span class="n">suc</span> <span
            class="o">=</span> <span class="n">first</span>
    <span class="k">return</span> <span cla