Columbia subject headings:
Harvard subject headings:
Labor unions--France--History--20th century--Congresses.
Labor unions--Germany--History--20th century--Congresses.
Working class--France--History--20th century--Congresses.
Working class--Germany--History--20th century--Congresses.
Princeton subject headings:
Labor unions--France--History--20th century--Congresses.
Labor unions--Germany--History--20th century--Congresses.
Working class--France--History--20th century--Congresses.
Working class--Germany--History--20th century--Congresses.