Columbia subject headings:
Music theater--20th century--History and criticism--Congresses.
Opera--20th century--Congresses.
Opera--Stage-setting and scenery--Congresses.
Harvard subject headings:
Music theater--20th century--History and criticism--Congresses.
Opera--20th century--Congresses.
Opera--Stage-setting and scenery--Congresses.
Princeton subject headings:
Music theater--20th century--History and criticism--Congresses.
Opera--20th century--Congresses.
Opera--Stage setting and scenery--Congresses.