Weale, Putnam
Macmillan, 1997
Buku Teks SO
Clyde, Paul Hibbert
Prentice-Hall, 1953
Buku Teks
Walker, Allan S.
Australian War Memorial, 1956
Buku Teks SO
Europe Publications Limited, 1992
Buku Referensi
Thompson, Warren S.
The University of Chicago Press, 1959
Buku Teks SO