Columbia subject headings:
Gregorian chants--History and criticism.
Sequences (Music)--History and criticism.
Tropes (Music)--History and criticism.
Harvard subject headings:
Church music--Catholic Church
Gregorian chants--History and criticism.
Princeton subject headings:
Gregorian chants--History and criticism.
Sequences (Music)--History and criticism.
Tropes (Music)--History and criticism.