Heffernan, James A.W., author
W.W. Norton & Company, 1986
Buku Referensi
Sheehan, Michael, author
Prentice-Hall, 1991
Buku Referensi
Bowden, Edwin T., author
Holt, Rinehart and Winston, 1963
Buku Teks
Aitchison, James, author
Cassell, 1994
Buku Teks
Schiffhorst, Gerald J., author
McGraw-Hill, 1991
Buku Referensi