One or more of the preceding sentences incorporates text from a publication now in the public domain: Oestreich, Thomas (1913). "Pope St. Gregory VII". In Herbermann, Charles (ed.). Catholic Encyclopedia. New York: Robert Appleton Company.
De Montclos, J. (1971). Lanfranc et Bérenger. La controverse eucharistique du XIe siècle. Leuven. OCLC542116.{{cite book}}: CS1 maint: location missing publisher (link)