Columbia subject headings:
Catholic Church--Liturgy--Congresses.
Divine office (Music)--History and criticism.
Gregorian chants--500-1400--Congresses.
Harvard subject headings:
Catholic Church--Liturgy--Congresses.
Divine office (Music)--History and criticism.
Gregorian chants--History and criticism.
Princeton subject headings:
Catholic Church--Liturgy--Congresses.
Divine office (Music)--History and criticism.
Gregorian chants--500-1400--Congresses.