Columbia subject headings:
Communism--Congresses.
Communism--Poland--Congresses.
Communism--Soviet Union--Congresses.
Harvard subject headings:
Communism--Congresses
Communism--Poland--Congresses.
Communism--Soviet Union--Congresses
Princeton subject headings:
Communism--Congresses.
Communism--Poland--Congresses.
Communism--Soviet Union--Congresses.