Columbia subject headings:
Harvard subject headings:
Espionage, West German--Germany (East)--History.
Germany (East)--Emigration and immigration--History.
Germany (West)--Emigration and immigration--History.
Spies--Germany (East)
Princeton subject headings:
Germany (East)--Emigration and immigration.
Germany (West)--Emigration and immigration.
Spies--Germany, East.