    /*
     * call-seq:
     *  -(node_set)
     *
     *  Difference - returns a new NodeSet that is a copy of this NodeSet, removing
     *  each item that also appears in +node_set+
     */
    static VALUE minus(VALUE self, VALUE rb_other)
    {
      xmlNodeSetPtr node_set;
      xmlNodeSetPtr other;
      xmlNodeSetPtr new;
      int j ;

      if(! rb_funcall(rb_other, rb_intern("is_a?"), 1, cNokogiriXmlNodeSet))
        rb_raise(rb_eArgError, "node_set must be a Nokogiri::XML::NodeSet");

      Data_Get_Struct(self, xmlNodeSet, node_set);
      Data_Get_Struct(rb_other, xmlNodeSet, other);

      new = xmlXPathNodeSetMerge(NULL, node_set);
      for (j = 0 ; j < other->nodeNr ; ++j) {
        xmlXPathNodeSetDel(new, other->nodeTab[j]);
      }

      return Nokogiri_wrap_xml_node_set(new);
    }