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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 graph(self):
 """ A conjunctive graph of all statements in the current instance. """

        if not hasattr(self, '_graph') or self._graph is None:
            self._graph = ConjunctiveGraph(store=self.store,
                                           identifier=self.base_uri)
        return self._graph