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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def advance_to(self, timestamp):
 """Advance the time reference so that now is the given timestamp. :param `float` timestamp: the new current timestamp. :raise `ValueError`: if *timestamp* is in the past. """

        now = self.__original_time()
        if timestamp < now:
            raise ValueError("cannot retreat time reference: "
                             "target {} < now {}"
                             .format(timestamp, now))
        self.__delta = timestamp - now