an>

<span class="sd">        :param px:the item set px</span>
<span class="sd">        :type px:FFI-List</span>
<span class="sd">        :param py:item set py</span>
<span class="sd">        :type py:FFI-List</span>
<span class="sd">        :return :the item set of pxy(px and py)</span>
<span class="sd">        :rtype :FFI-List</span>
<span class="sd">        &quot;&quot;&quot;</span>
        <span class="n">pxyUL</span> <span class="o">=</span> <span class="n">_FFList</span><span class="p">(</span><span c