n">elements</span><span class="o">=</span><span class="kc">None</span><span class="p">):</span>
        <span class="sd">&quot;&quot;&quot;</span>
<span class="sd">        Identify Carbon atoms in the MoleculeGraph that fit the characteristics</span>
<span class="sd">        defined Ertl (2017), returning a list of their node indices.</span>

<span class="sd">        The conditions for marking carbon atoms are (quoted from Ertl):</span>
<span class="sd">            &quot;- atoms connected by non-aromatic do