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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 _find_base_version_ids(self, symbol, version_ids):
 """ Return all base_version_ids for a symbol that are not bases of version_ids """

        cursor = self._versions.find({'symbol': symbol,
                                      '_id': {'$nin': version_ids},
                                      'base_version_id': {'$exists': True},
                                      },
                                     projection={'base_version_id': 1})
        return [version["base_version_id"] for version in cursor]