Columbia subject headings:
Coal trade--Germany.
Germany--Economic conditions--1918-1945.
Industries--Germany--North Rhine-Westphalia.
Steel industry and trade--Germany.
Harvard subject headings:
Coal trade--Germany
Germany--Economic conditions--1918-1945.
Industries--Germany--North Rhine-Westphalia.
Steel industry and trade--Germany
Princeton subject headings:
Coal trade--Germany.
Germany--Economic conditions--1918-1945.
Industries--Germany--North Rhine-Westphalia.
Steel industry and trade--Germany.