Robinson, David, author
University Park Press, 1979
Buku Teks
general editors Michael Orme, Susanna Graham-Jones
Penguin Group, 1989
Buku Referensi
Bansal, H.L., author
B. Jain Publisher, 1989
Buku Teks
Clinard, Marshall B. (Marshall Barron), author
Tree Press, 1966
Buku Teks
French, F. G., author
Oxford University Press, 1947
Buku Teks