Sets the chunk backward from this chunk in the list of free chunks.

        :param bck: the chunk to precede this chunk in the list of free chunks

def set_bck_chunk(self, bck):
        """
        Sets the chunk backward from this chunk in the list of free chunks.

        :param bck: the chunk to precede this chunk in the list of free chunks
        """
        raise NotImplementedError("%s not implemented for %s" % (self.set_bck_chunk.__func__.__name__,
                                                                 self.__class__.__name__))