Ashley, Ruth
John Wiley & Sons, 1980
Buku Teks SO
edited by R.C. Olby, G.N. Cantor, J.R.R. Christie and M.J.S. Hodge
Routledge, 1990
Buku Referensi
edited by William Bechtel and George Graham
Blackwell, 1999
Buku Teks SO
Stathis Psillos, Martin Curd, editor
Routledge, 2008
Buku Teks
Dunlop, David L.
Prentice-Hall, 1983
Buku Teks SO