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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 trunking(self):
 """ Access the Trunking Twilio Domain :returns: Trunking Twilio Domain :rtype: twilio.rest.trunking.Trunking """

        if self._trunking is None:
            from twilio.rest.trunking import Trunking
            self._trunking = Trunking(self)
        return self._trunking