Artikel Jurnal
Thakur, Ramesh
London: Westview Press, 1986,
Buku Referensi
Spate, Oskar Hermann Kristian, author
Oxford University Press, 1965
Buku Teks
Warnecke, Andrea, author
Profiles Publishing, 2000
Buku Teks
Higgins, P. F. P.
Butterworth, 1974
Buku Teks