Friedrich, Carl J.
Harvard University, 1958
Buku Teks
Sennett, Richard
Alfred A. Knopf, 1980
Buku Teks SO
editor, Frederick G. Ruffner, Ann C. Thomas, Ann Underwood, Mangoret Fisk, Harold C. Young
Gale Research, 1964
Buku Referensi
edited by Robin Middleton
MIT Press, 1996
Buku Teks SO
Eddey, Peter H.
Prentice-Hall, 1988
Buku Teks