Schmidt, Erich W.
Pergamon Press , 1974
Buku Teks SO
John Wiley & Sons, 1969
Buku Teks SO
Hasugian, Rudy
Universitas Indonesia, 2007
UI - Skripsi Membership
Dykstra, Clifford E.
Prentice-Hall, 1997
Buku Teks SO
Billington, E.W.
McGraw-Hill International Book Company, 1981
Buku Teks SO