Columbia subject headings:
Opera--19th century.
Verdi, Giuseppe, 1813-1901. Operas.
Wagner, Richard, 1813-1883. Operas.
Harvard subject headings:
Opera--19th century
Verdi, Giuseppe, 1813-1901. Operas.
Wagner, Richard, 1813-1883. Operas.
Princeton subject headings:
Opera--19th century.
Verdi, Giuseppe, 1813-1901. Operas.
Wagner, Richard, 1813-1883. Operas.