Given a list of lists, and a number of new lists to add, copy the
    content of the first list into the new ones, and add them to the list
    of lists.

def _grow(list_of_lists, num_new):
    """ Given a list of lists, and a number of new lists to add, copy the
    content of the first list into the new ones, and add them to the list
    of lists.
    """
    first = list_of_lists[0]
    for i in range(num_new):
        list_of_lists.append(copy.deepcopy(first))
    return list_of_lists