Columbia subject headings:
Harvard subject headings:
Coal mines and mining--Germany--Westphalia--History--Sources.
Electric power-plants--Germany--Westphalia--History.
Miners--Labor unions--Germany--Westphalia--History--Sources.
Vereinigte Elektrizitätswerke Westfalen--History--Sources.
Princeton subject headings:
Coal mines and mining--Germany--Westphalia--History--Sources.
Electric utilities--Germany--Westphalia--History--Sources.
Miners--Labor unions--Germany--Westphalia--History--Sources.
Vereinigte Elektrizitätswerke Westfalen--History--Sources.