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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 document_ids(self):
 """returns a list of document IDs used in the PCC"""

        matches = [PCC_DOCID_RE.match(os.path.basename(fname))
                   for fname in pcc.tokenization]
        return sorted(match.groups()[0] for match in matches)