Wolff, John U., compiler
Cornell University, 1972
Buku Referensi
Halm, George N.
Feffer and Simons, 1971
Buku Teks SO
Maddi, Salvatore R.
The Dassey Press, 1968
Buku Teks SO
Tade Matthias Spranger
Springer, 2012
eBooks
edited by John D. Lees and Malcolm Shaw
Duke University Press, 1979
Buku Teks SO