Stalk, George Jr
The Free Press, 1990
Buku Teks
Bateman, Thomas S., author
McGraw-Hill, 2002
Buku Teks
Kuczmarski, Thomas D., author
Prentice-Hall, 1988
Buku Teks
Fakhraddin Maroofi, author
University of Kurdistan, 2015
Artikel Jurnal
Hill, Charles W. L., author
McGraw-Hill, 1997
Buku Teks