Columbia subject headings:
North Rhine-Westphalia (Germany)--Economic conditions--Sources.
North Rhine-Westphalia (Germany)--Social conditions--Sources.
Working class--Germany--North Rhine-Westphalia--History--Sources.
Harvard subject headings:
North Rhine-Westphalia (Germany)--Economic conditions--Sources.
North Rhine-Westphalia (Germany)--Social conditions--Sources.
Working class--Germany--North Rhine-Westphalia--History--Sources.
Princeton subject headings:
Westphalia (Germany)--Economic conditions.
Westphalia (Germany)--History--Sources.
Westphalia (Germany)--Social conditions.