def equality(iterable: list) -> bool:
    """
    Check equality of ALL elements in an interable.
    >>> equality([1, 2, 3, 4])
    False
    >>> equality([2, 2, 2, 2])
    True
    >>> equality([1, 2, 3, 2, 1])
    False
    """
    return len(set(iterable)) in (0, 1)