Engert, M. (1969). Problems of Long-term Planning in the German Democratic Republic. The Institute of National Planning.
Lua i Stíl Chicago (17ú heag.)Engert, Manfred. Problems of Long-term Planning in the German Democratic Republic. Cairo: The Institute of National Planning, 1969.
Lua MLA (9ú heag.)Engert, Manfred. Problems of Long-term Planning in the German Democratic Republic. The Institute of National Planning, 1969.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.