def helper_copysign(f, unit1, unit2):
    if (unit1 is None):
        return ([None, None], None)
    else:
        return ([None, None], unit1)
def helper_copysign(f, unit1, unit2):
    if (unit1 is None):
        return ([None, None], None)
    else:
        return ([None, None], unit1)