>vertices</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>

    <span class="k">def</span> <span class="nf">rank_increase</span><span class="p">(</span><span class="n">seen</span><span class="p">,</span> <span class="n">candidate</span><span class="p">):</span>

        <span class="n">rank0</span> <span class="o">=</span> <span class="nb">len</span><span class="p">(</span><span class="n">seen</span><span class="p">)</span> <span class="o">-</span> <span class="mi">1</span>
 