Spear, Percival
The University of Michigan Press, 1961
Buku Teks
Rybak, Stephanie
Macmillan, 1985
Buku Teks
Williams, Gareth
PSI, [date of publication not identified]
Buku Teks
Sastri, K.A. Nilakanta
University of Madras, 1946
Buku Teks
Sydsæter, Knut
Prentice-Hall, 2008
Buku Teks