Littler, John
Cambridge University Press, 1984
Buku Teks
Levy, Matthys
W.W. Norton & Co., 1992
Buku Teks
Oxford University Press, 1977
Buku Teks
Baron, Stephen L., editor
Prentice-Hall, 1978
Buku Referensi
Allen, Edward, author
Oxford University Press, 2005
Buku Teks