↑ J.N.D. Kelly, Oxford Dictionary of the Popes, p. 227
The Three Popes: An Account of the Great Schism, by Marzieh Gail.
The Great Schism: 1378, by John Holland Smith (New York 1970).
The Origins of the Great Schism: A study in fourteenth century ecclesiastical history, by Walter Ullmann (Hamden, Conn: Archon Books, 1967 (rev. of 1948 original publication)).
