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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 enquire_graph(self, graph=None):
 """ Verifies and returns relevant TensorFlow graph. If non-None graph were passed, the same graph is returned. Otherwise, nodes's graph is exposed and it is undefined the default TensorFlow graph is used. :param graph: TensorFlow graph or None. Default is None. :return: TensorFlow graph. """

        if graph is None:
            graph = self.root.graph if self.graph is None else self.graph
            if graph is None:
                graph = tf.get_default_graph()
        return graph