Columbia subject headings:
Leoncavallo, Ruggiero, 1858-1919--Congresses.
Opera--Italy--19th century--Congresses.
Harvard subject headings:
Leoncavallo, Ruggiero, 1858-1919--Congresses.
Opera--Italy--19th century--Congresses.
Princeton subject headings:
Leoncavallo, Ruggiero, 1858-1919--Congresses.
Opera--Italy--19th century--Congresses.