Murray, Peter
Murray, 2014
Buku Referensi
Craven, Paul R.
Dickenson Publishing, 1968
Buku Teks SO
Bennett, A. Gordon
Gloucester, Mass, 1980
Buku Teks SO
Griffith University,
Majalah, Jurnal, Buletin
Peeters, BenoƮt, 1956-
Polity Press, 2013
Buku Teks SO