Greenfield, Jeanette
Cambridge University Press , 1995
Buku Teks
Churchill, R.R.
Manchester University Press, 1992
Buku Teks
Mas Achmad Santosa
2005
Artikel Jurnal
Andrassy, Juraj
Columbia University Press, 1970
Buku Teks
Colombos, C. John
Longman, 1959
Buku Teks