Columbia subject headings:
Harvard subject headings:
Guido, d'Arezzo--Congresses.
Music theorists--Italy--Biography--Congresses.
Music theory--History--500-1400--Congresses.
Music--History and criticism--500-1400--Congresses.
Princeton subject headings:
Guido, d'Arezzo--Congresses.
Music theory--History--500-1400--Congresses.