Columbia subject headings:
Harvard subject headings:
Mines and mineral resources--Germany--Rhein-Sieg-Kreis--History.
Rhein-Sieg-Kreis (Germany)--Economic conditions.
Rhein-Sieg-Kreis (Germany)--History.
Princeton subject headings:
Mines and mineral resources--Germany--Rhein-Sieg-Kreis--History.
Rhein-Sieg-Kreis (Germany)--Economic conditions.
Rhein-Sieg-Kreis (Germany)--History.