s="n">atom</span><span class="p">]</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">)[</span><span class="mi">0</span><span class="p">])</span><span class="o">.</span><span class="n">union</span><span class="p">(</span><span class="n">atom_cluster</span><span class="p">)</span>
        <span class="n">atom_cluster</span> <span class="o">=</span> <span class="n">new_cluster</span>
        <span class="k">for</span> <span class="n">new_atom</span> <span class="ow">in</span> <span clas