Columbia subject headings:
Catholic Church--Doctrines.
Catholic Church--Relations--Orthodox Eastern Church.
Orthodox Eastern Church--Doctrines.
Orthodox Eastern Church--Relations--Catholic Church.
Harvard subject headings:
Church history--Primitive and early church, ca. 30-600
Princeton subject headings:
Catholic Church--Doctrines.
Catholic Church--Relations--Orthodox Eastern Church.
Orthodox Eastern Church--Doctrines.
Orthodox Eastern Church--Relations--Catholic Church.