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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 fax(self):
 """ Access the Fax Twilio Domain :returns: Fax Twilio Domain :rtype: twilio.rest.fax.Fax """

        if self._fax is None:
            from twilio.rest.fax import Fax
            self._fax = Fax(self)
        return self._fax