Columbia subject headings:
Musical theater--Austria--Vienna--Congresses.
Musical theater--Hungary--Budapest--Congresses.
Opera--Austria--Vienna--Congresses.
Opera--Hungary--Budapest--Congresses.
Harvard subject headings:
Musical theater--Austria--Vienna--Congresses.
Musical theater--Hungary--Budapest--Congresses.
Opera--Austria--Vienna--19th century.
Opera--Austria--Vienna--20th century.
Opera--Austria--Vienna--Congresses.
Opera--Hungary--Budapest--19th century.
Opera--Hungary--Budapest--20th century.
Opera--Hungary--Budapest--Congresses.
Princeton subject headings:
Musical theater--Austria--Vienna--Congresses.
Musical theater--Hungary--Budapest--Congresses.
Opera--Austria--Vienna--Congresses.
Opera--Hungary--Budapest--Congresses.