Singh, U.K.
Anmol Publications, 1998
Buku Referensi
edited by Muriel Albers Bittel, Lester Robert Bittel and Jackson Eugene Ramsey
Grolier International, 1995
Buku Referensi
Allen, David
Crest Publishing House, 2002
Buku Teks
David, Fred R.
Merill, 1989
Buku Teks
Wright, Peter
Allyn and Bacon, 1992
Buku Teks