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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 exist_node(self, graph, node, branch, turn, tick, extant):
 """Declare that the node exists or doesn't. Inserts a new record or updates an old one, as needed. """

        if (branch, turn, tick) in self._btts:
            raise TimeError
        self._btts.add((branch, turn, tick))
        self._nodes2set.append((self.pack(graph), self.pack(node), branch, turn, tick, extant))