Columbia subject headings:
Gregor, Joseph, 1888-1960--Congresses.
Librettists--Austria--Congresses.
Literary historians--Austria--Congresses.
Harvard subject headings:
Gregor, Joseph, 1888-1960--Congresses.
Librettists--Austria--Congresses.
Literary historians--Austria--Congresses.
Princeton subject headings:
Gregor, Joseph, 1888-1960--Congresses.
Librettists--Austria--Congresses.