Joel S. Panzer, The Popes and Slavery, Staten Island, New York, Society of St. Paul, 1996, pp.89-91. van Helden, Al (1995).
2007년 6월 7일에 확인함.  Joel S. Panzer, The Popes and Slavery, Staten Island, New York, Society of St. Paul, 1996, pp.89-91. van Helden, Al (1995).