Halpern, Manfred
Princeton University Press, 1963
Buku Teks SO
Artikel Jurnal
edited by Christian P. Potholm and Richard A. Fredland
University Press of America, 1980
Buku Teks
Macneil, Ian R.
[Publisher not identified], 1966
Buku Teks
Europa Publications Limited, 1991
Buku Referensi