Columbia subject headings:
Catholic Church--Relations--Orthodox Eastern Church--Sources.
Orthodox Eastern Church--Relations--Catholic Church--History--Sources.
Union of Brest--Sources.
Harvard subject headings:
Belarus--Church history--Sources.
Union of Brest
Princeton subject headings:
Belarus--Church history--Sources.
Catholic Church--Byzantine rite, Ruthenian--History--Sources.
Ukraine--Church history--Sources.
Union of Brest--Sources.