Columbia subject headings:
Ambrose, Saint, Bishop of Milan, -397.
Church music--Catholic Church.
Gregorian chants--History and criticism.
Harvard subject headings:
Ambrose, Saint, Bishop of Milan, -397
Church music--Catholic Church
Gregorian chants--History and criticism.
Princeton subject headings:
Ambrose, Saint, Bishop of Milan, -397.
Church music.
Gregorian chants--History and criticism.