Columbia subject headings:
Harvard subject headings:
Industries--Germany--Krefeld--History--Congresses.
Industries--Germany--Rhineland--History--Congresses.
Krefeld (Germany)--History--Congresses.
Rhineland (Germany)--History--Congresses.
Princeton subject headings:
Industries--Germany--Krefeld--History--Congresses.
Industries--Germany--Rhineland--History--Congresses.
Krefeld (Germany)--History--Congresses.
Rhineland (Germany)--History--Congresses.