Herman, A.L.
Westview Press, 1991
Buku Referensi
Winzeler, Robert L.
Lanham Rowman & Littlefield, 2016
Buku Teks SO
Ratnakar, Pramesh
Tiger Books International, 1996
Buku Teks SO
Feuchtwang, Stephan
Curzon Press , 2001
Buku Teks SO
Bruun, Ole
NIAS Press, 2011
Buku Teks SO