Cowen, Zelman, author
North-Western University Press, 1965
Buku Teks
Austin, Dennis
Routledge , 1922
Buku Teks
Odhe, Thersten
Cooperative Lague of the USA, 1960
Buku Teks
Qureshi, Anwar Iqbal
Oxford University Press, 1947
Buku Teks
The Association of Commonwealth Universities,
Buku Referensi