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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 end_before(self, document_fields):
 """End query before a cursor with this collection as parent. See :meth:`~.firestore_v1beta1.query.Query.end_before` for more information on this method. Args: document_fields (Union[~.firestore_v1beta1.\ document.DocumentSnapshot, dict, list, tuple]):
 a document snapshot or a dictionary/list/tuple of fields representing a query results cursor. A cursor is a collection of values that represent a position in a query result set. Returns: ~.firestore_v1beta1.query.Query: A query with cursor. """

        query = query_mod.Query(self)
        return query.end_before(document_fields)