Columbia subject headings:
Constantinople (Ecumenical patriarchate)--Bishops--Biography.
Constantinople (Ecumenical patriarchate)--Doctrines.
Holy Spirit--Procession.
Istanbul (Turkey)--Biography.
Orthodox Eastern Church--Doctrines.
Orthodox Eastern Church--Turkey--Istanbul--Bishops--Biography.
Photius I, Saint, Patriarch of Constantinople, approximately 820-approximately 891.
Harvard subject headings:
Constantinople (Ecumenical patriarchate)--Bishops--Biography.
Constantinople (Ecumenical patriarchate)--Doctrines.
Holy Spirit--Procession
Holy Spirit--Procession--History of doctrines--Middle Ages, 600-1500.
Mystagogy--Orthodox Eastern Church--History of doctrines--Middle Ages, 600-1500.
Orthodox Eastern Church--Doctrines--History.
Orthodox Eastern Church--Doctrines.
Princeton subject headings: