Westview Press, 1980
Buku Teks
Gsovski, Vladimir
Atlantic Books, 1959
Buku Teks
by the Economist Intelligence Unit and the Cartographic Dept. of the Clarendon Press
Oxford University Press, 1956
Buku Referensi
edited by John Odmark
John Benjamins B.V. , 1979/1980/1981/1982
Buku Teks
Atlantic Books, 1959
Buku Teks