Munchen Carl Hanser Verlag 1974
Buku Teks
Hudson, William Henry
London George G. Harrap 1913
Buku Referensi
Oregon : University of Oregon
Majalah, Jurnal, Buletin
Marcus, Aage
Zurich Atlantis Verlag 1949
Buku Teks
Peer, Willie van
Routledge, 1991
Buku Teks SO