Columbia subject headings:
Germany (East)--History--Congresses.
Germany (East)--Relations--Poland--Congresses.
Poland--Relations--Germany (East)--Congresses.
Harvard subject headings:
Germany (East)--History--Congresses.
Germany (East)--History.
Germany (East)--Relations--Poland--Congresses.
Poland--Relations--Germany (East)--Congresses.
Princeton subject headings: