code: def _filter_gte(self, term, field_name, field_type, is_not):
          
          vrp = XHValueRangeProcessor(self.backend)
          pos, begin, end = vrp('%s:%s' % (field_name, _term_to_xapian_value(term, field_type)), '*')
          if is_not:
              return xapian.Query(xapian.Query.OP_AND_NOT,
                                  self._all_query(),
                                  xapian.Query(xapian.Query.OP_VALUE_RANGE, pos, begin, end)
                                  )
          return xapian.Query(xapian.Query.OP_VALUE_RANGE, pos, begin, end)
docs: Private method that returns a xapian.Query that searches for any term
          that is greater than `term` in a specified `field`.