def occupied_by_sort(self, address):
        idx = self._search(address)
        if len(self._list) <= idx:
            return None
        if self._list[idx].start <= address < self._list[idx].end:
            return self._list[idx].sort
        if idx > 0 and address < self._list[idx - 1].end:
            return self._list[idx - 1].sort
        return None