Lensen, George Alexander, author
Sophia University, 1970
Buku Teks
Rothstein, Andrew, author
Penguin Books , 1950
Buku Teks
Mongait, Alexander, author
Foreign Languages Publishing House, 1959
Buku Teks
Munich : Institute for the Study of the USSR
Majalah, Jurnal, Buletin
by the Economist Intelligence Unit and the Cartographic Dept. of the Clarendon Press
Oxford University Press, 1956
Buku Referensi