Columbia subject headings:
Councils and synods.
Orthodox Eastern Church--Relations--Catholic Church.
Harvard subject headings:
Catholic Church--Europe, Eastern--History.
Catholic Church--Oriental rites.
Catholic Church--Relations--Orthodox Eastern Church--History--Congresses.
Orthodox Eastern Church--Relations--Catholic Church--History--Congresses.
Schism--Eastern and Western Church.
Princeton subject headings:
Orthodox Eastern Church--Congresses.