Northcott, C.H.
Philoshopical Library , 1956
Buku Teks
Flippo, Edwin B., author
McGraw-Hill, 1984
Buku Teks
Armstrong, Michael, author
Kogan Page Limited, 1995
Buku Referensi
Heckman, I. L., author
Charles E. Merrill, 1962
Buku Teks
Schleh, Edward C., author
Prentice-Hall, 1958
Buku Teks