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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 get_root_subject(self):
        'Returns the BNode which describes the topmost subject of the graph.'

        manifest = URIRef(self.manifest)

        if list(self.rdf.triples((manifest, None, None))):
            return manifest
        else:
            return self.rdf.subjects(None, self.manifest).next()