Columbia subject headings:
Catholic Church--Relations--Lutheran Church.
Lutheran Church--Relations--Catholic Church.
Papacy and Christian union.
Papacy--Controversial literature.
Popes--Infallibility--History of doctrines.
Harvard subject headings:
Papacy.
Princeton subject headings:
Catholic Church--Relations--Lutheran Church.
Lutheran Church--Relations--Catholic Church.
Papacy and Christian union--History.