n class="o">+</span><span class="w"> </span><span class="mi">2</span><span class="o">*</span><span class="n">xdel</span><span class="p">;</span>
<span class="o">...</span><span class="p">;</span>

<span class="n">the</span><span class="w"> </span><span class="n">last</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="n">interval</span><span class="w"> </span><span class="k">is</span><span class="w"> </span><span class="n">from</span><span class="w"> </span><span c