Columbia subject headings:
Harvard subject headings:
Archives--Germany--North Rhine-Westphalia--History--Congresses.
North Rhine-Westphalia (Germany)--Economic conditions--Sources--Congresses.
North Rhine-Westphalia (Germany)--History--Sources--Congresses.
Princeton subject headings:
Archives--Germany--North Rhine-Westphalia--History--Congresses.
North Rhine-Westphalia (Germany)--Economic conditions--Sources--Congresses.
North Rhine-Westphalia (Germany)--History--Sources--Congresses.