Columbia subject headings:
Agnus Dei (Music)--History and criticism.
Church music--Catholic Church.
Gregorian chants--History and criticism.
Mass (Music)
Harvard subject headings:
Agnus Dei (Music)--History and criticism.
Church music--500-1400.
Church music--Catholic Church
Princeton subject headings:
Agnus Dei (Music)--History and criticism.
Church music--Catholic Church.
Church music--Medieval.