            <span class="kd">::</span> <span class="n">pp</span>
  <span class="c">!! Particle iterator.</span>
  <span class="kt">INTEGER</span>                                                <span class="kd">::</span> <span class="n">ss</span>
  <span class="c">!! Species iterator.</span>

  <span class="k">if</span> <span class="p">(</span><span class="n">size</span><span class="p">(</span><span class="n">Y</span><span class="p">,</span><span class="mi">1</span><span class="p">).</span><span class="n">eq