Columbia subject headings:
Communism--Germany--History--Sources.
Communism--Poland--History--Sources.
International labor activities--History--Sources.
Labor--Germany--History--Sources.
Labor--Poland--History--Sources.
Harvard subject headings:
Communism--Germany--History--Sources.
Communism--Poland--History--Sources.
International labor activities--History--Sources.
Working class--Germany--History--Sources.
Working class--Poland--History--Sources.
Princeton subject headings:
Communism--Germany--History--Sources.
Communism--Poland--History--Sources.
International labor activities--History--Sources.
Working class--Germany--History--Sources.
Working class--Poland--History--Sources.