Bois, W.E.B. Du
Harcourt, Brace and Company, 1945
Buku Teks
Havinden, Michael, author
Routledge, 1993
Buku Teks
Walker, Gordon, author
McGraw-Hill-Irwin, 2004
Buku Teks
Walker, Warren F.
Saunders College, 1980
Buku Teks
Walker, Robert A.
The Dryden Press, 1953
Buku Teks