@classmethod
def change_repr(cls, representation=None):
    """Toggles globally between cycle notation or one-line notation. Note
        that internal representation is still one-line."""
    L = ['oneline', 'cycle', 'both']
    if representation in L:
        cls._REPR = representation
    else:
        k = int(input('1 for oneline, 2 for cycle, 3 for both\n '))
        k -= 1
        cls._REPR = L[k]
