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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 url(self):
 """ URL of document on ProvStore :Example: 'https://provenance.ecs.soton.ac.uk/store/documents/148' """

        if not self.abstract:
            return "%s/documents/%i" % ("/".join(self._api.base_url.split("/")[:-2]), self.id)