Columbia subject headings:
Harvard subject headings:
Escapes--Germany (East)
Germany (East)--Boundaries.
Germany (East)--History.
Hoer, Manfred.
Hoer, Peter.
Political persecution--Germany (East)
Political refugees--Germany (East)--Biography.
Schopf, Peter.
Tunnels--Germany (East)
Princeton subject headings:
Hoër, Manfred.