Columbia subject headings:
Europe--In literature--Congresses.
European drama--History and criticism--Congresses.
Opera--Congresses.
Theater--History--Congresses.
Harvard subject headings:
Europe--In literature--Congresses.
European drama--History and criticism--Congresses.
Opera--Congresses
Theater--History--Congresses.
Princeton subject headings:
Europe--In literature--Congresses.
European drama--History and criticism--Congresses.
Opera--Congresses.
Theater--History--Congresses.