Columbia subject headings:
Harpener Bergbau-Aktiengesellschaft.
Mine buildings--Germany--Ruhr (Region)--History.
Mines and mineral resources--Germany--Ruhr (Region)
Harvard subject headings:
Harpener Bergbau-Aktiengesellschaft.
Mine buildings--History.
Mines and mineral resources--Germany--Ruhr (Region)
Princeton subject headings:
Harpener Bergbau-Aktiengesellschaft.
Mine buildings--Germany (West)--Ruhr (Region)--History.
Mines and mineral resources--Germany (West)--Ruhr (Region).