Bernard, Hugh Y.
Oceania Publications, Inc., 1968
Buku Teks
Cayer, N. Joseph., author
Wadsworth/Thomson Learning, 2004
Buku Teks
Vanguard , 1963
Buku Teks
Hart, James, author
The Johns Hopkins Press, 1930
Buku Teks
Jones, Vernon Dale, author
M.E. Sharpe, 1998
Buku Teks