Columbia subject headings:
Harvard subject headings:
Germany (East)--History--Sources.
Germany (East). Ministerium für Staatssicherheit--History.
Postal service--Censorship--Germany (East)--History--20th century--Sources.
Secret service--Germany (East)--History--Sources.
Princeton subject headings:
Germany (East). Ministerium für Staatssicherheit--History.
Postal service--Censorship--Germany (East)--History.