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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 trie(self):
 """ A property to link into IntentEngine's trie. warning:: this is only for backwards compatiblility and should not be used if you intend on using domains. Return: the domains trie from its IntentEngine """

        domain = 0
        if domain not in self.domains:
            self.register_domain(domain=domain)
        return self.domains[domain].trie