Columbia subject headings:
Operas--Analysis, appreciation--Congresses.
Verdi, Giuseppe, 1813-1901. Operas--Congresses.
Wagner, Richard, 1813-1883. Operas--Congresses.
Harvard subject headings:
Operas--Analysis, appreciation--Congresses.
Verdi, Giuseppe, 1813-1901. Operas--Congresses.
Wagner, Richard, 1813-1883. Operas--Congresses.
Princeton subject headings:
Operas--Analysis, appreciation.
Verdi, Giuseppe, 1813-1901. Operas.
Wagner, Richard, 1813-1883. Operas.