Columbia subject headings:
Harvard subject headings:
Coal mines and mining--Germany--History--Congresses.
ESPAG--History--Congresses.
Lignite industry--Germany--Lower Lusatia--History--Congresses.
Lignite--Refining--Germany--Lower Lusatia--History--Congresses.
Princeton subject headings:
Coal mines and mining--Germany--History--Congresses.
ESPAG--History--Congresses.
Lignite industry--Germany--Lower Lusatia--History--Congresses.
Lignite--Refining--Germany--Lower Lusatia--History--Congresses.