Columbia subject headings:
Libretto--Congresses.
Music and language--Congresses.
Music and literature--Italy--History--Congresses.
Opera--Italy--Congresses.
Harvard subject headings:
Libretto--Congresses.
Opera--Congresses
Princeton subject headings:
Conference papers and proceedings.
Libretto--Congresses.
Music and literature--Congresses.
Opera--Congresses.