Columbia subject headings:
Sports--Germany--Ruhr (Region)--History.
Working class--Germany--Ruhr (Region)--Social life and customs.
Working class--Recreation--Germany--Ruhr (Region)--History.
Harvard subject headings:
Sports--Germany--Ruhr (Region)--History.
Working class--Germany--Ruhr (Region)--Social life and customs.
Working class--Recreation--Germany--Ruhr (Region)--History.
Princeton subject headings:
Labor movement--Germany--Ruhr (Region)--History.
Working class--Germany--Ruhr (Region)--Recreation--History.