@staticmethod
def _tauband(generator, n, power=1):
    """
        Transformation: generator --> t^{power}(generator)

        Where:          generator * D = D * t(generator)
        Modifies a 2-element list in place. No error checks.

        >>> a = [1, 5]
        >>> Braid._tauband(a, 5)
        >>> a
        [1, 2]
        >>> Braid._tauband(a, 7, -3)
        >>> a
        [5, 6]
        """
    if power == 0:
        return
    generator[0] += power
    generator[1] += power
    positivity = generator[0] > generator[1]
    generator[0] = (generator[0] - 1) % n + 1
    generator[1] = (generator[1] - 1) % n + 1
    if positivity != (generator[0] > generator[1]):
        generator.reverse()
