Columbia subject headings:
Gregorian chants--History and criticism--Congresses.
Musical books--History--16th century--Congresses.
Musical books--History--To 1500--Congresses.
Harvard subject headings:
Gregorian chants--History and criticism--Congresses.
Musical books--History--16th century--Congresses.
Musical books--History--To 1500--Congresses.
Princeton subject headings:
Gregorian chants--History and criticism--Congresses.
Musical books--History--16th century--Congresses.
Musical books--History--To 1500--Congresses.