Gaer, Joseph
Dodd, Mead, 1956
Buku Teks SO
edited by Stewart Sutherland, Leslie Houlden, Peter Clarke, Friedhelm Hardy
Routledge, 1988
Buku Referensi
Burke, T. Patrick
Blackwell, 2005
Buku Teks SO
Ewing, J.H.
Dell Publishing, 1964
Buku Teks SO
edited by Peter Clarke
Routledge, 1988
Buku Teks SO