[, Springer], 2012
eBooks
Jones, Frank H.
W. Heffer & Sons, 1972
Buku Teks
New York, N.Y. : New York University Press, 1977,
Buku Teks
edited by Helmut Arntz
Press and Information Office of the Federal Government, 1961
Buku Teks SO
Konrad-Adenauer-Stiftung, 2014
Majalah, Jurnal, Buletin