Halliday, Fred, author
Cambridge University Press, 2005
Buku Teks
MEI Publications Ltd, 2008
Majalah, Jurnal, Buletin
Laqueur, Walter Z.
Routledge & Kegan Paul , 1959
Buku Teks
Grolier Incorporated, 1964
Buku Referensi
General Agreement on Tariffs and Trade, 1971
Buku Teks