class="k">for</span> <span class="n">node</span> <span class="ow">in</span> <span class="n">ring</span><span class="p">:</span>
                    <span class="k">if</span> <span class="n">node</span> <span class="ow">in</span> <span class="n">carbons</span><span class="p">:</span>
                        <span class="n">specials</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">node</span><span class="p">)</span>

        <span class="k">return</span> <span cl