West Publishing Co, 1993
Buku Referensi
Rodgers, William H.
[Publisher not identified], 1977
Buku Teks SO
Bockrath, Joseph T.
McGraw-Hill, 1977
Buku Teks
Tabb, William Murray
Michie, 1992
Buku Teks SO
Little,Brown and Company, [date of publication not identified]
Buku Teks