Columbia subject headings:
Organ (Musical instrument)--History--15th century.
Organ (Musical instrument)--History--Congresses.
Organ music--15th century--History and criticism.
Harvard subject headings:
Organ (Musical instrument)--History--15th century.
Organ (Musical instrument)--History--Congresses.
Organ music--History and criticism.
Princeton subject headings:
Organ (Musical instrument)--History--Congresses.
Organ music--15th century--Congresses.