Thakur, Ramesh
London: Westview Press, 1986,
Buku Referensi
Spate, Oskar Hermann Kristian, author
Oxford University Press, 1965
Buku Teks
Mulgan, Richard, author
Oxford University Press, 1989
Buku Teks
University of California Press, 1947
Buku Teks
Sinclair, Keith
Penguin Books, 1986
Buku Teks