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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 delete(self, reference, option=None):
 """Add a "change" to delete a document. See :meth:`~.firestore_v1beta1.document.DocumentReference.delete` for more information on how ``option`` determines how the change is applied. Args: reference (~.firestore_v1beta1.document.DocumentReference):
 A document reference that will be deleted in this batch. option (Optional[~.firestore_v1beta1.client.WriteOption]):
 A write option to make assertions / preconditions on the server state of the document before applying changes. """

        write_pb = _helpers.pb_for_delete(reference._document_path, option)
        self._add_write_pbs([write_pb])