Columbia subject headings:
Mozart, Wolfgang Amadeus, 1756-1791--Congresses.
Wagner, Richard, 1813-1883--Congresses.
Harvard subject headings:
Mozart, Wolfgang Amadeus, 1756-1791--Congresses.
Wagner, Richard, 1813-1883--Congresses.
Princeton subject headings:
Mozart, Wolfgang Amadeus, 1756-1791. Operas--Congresses.
Music--Philosophy and aesthetics--Congresses.
Opera--Congresses.
Wagner, Richard, 1813-1883. Operas--Congresses.