Columbia subject headings:
Harvard subject headings:
Heidelberg (Germany)--Social conditions.
Labor unions--Germany--Heidelberg--History--Sources.
Labor unions--Germany--Heidelberg--History.
Working class--Germany--Heidelberg--History.
Princeton subject headings:
Heidelberg (Germany)--Social conditions.
Labor movement--Germany (West)--Heidelberg--History.
Labor unions--Germany (West)--Heidelberg--History--Sources.
Labor unions--Germany (West)--Heidelberg--History.