Universe , 2004
Buku Teks
edited by Manjulika Dubey and Bikram Grewal
Hofer Press, 1992
Buku Referensi
Nyerere, Julius Kambarage
Oxford University Press, 1990
Buku Teks
Ashish, 1988
Buku Teks
Hesseline, William B.
Louisiana State university Press, 1949
Buku Teks