The concept of heresy in the Middle Ages (11th - 13th C.) : proceedings of the International Conference. Louvain, May 13-16, 1973 / edited by W. Lourdaux and D. Verhelst
. – Leuven : Leuven University Press, 1976
. – viii, 232 p. ; 25 cm
. – (Mediaevalia Lovaniensia. Series 1. Studia ; 4)