Robertson, Hector Menteith
Cambridge University Press, 1957
Buku Teks
Dyzenhaus, David
Oxford University Press , 1991
Buku Teks
Hofman, Michael
Oxford University Press, 2017
eBooks
Spooner, F.P.
Fredereck A.Praeger Publisher, 1960
Buku Teks
Beer, Credric de
Africa World, 1986
Buku Teks