Hicks, John R., author
The Clarendon Press, 1952
Buku Teks
Becker, William E., author
Prentice-Hall, 1971
Buku Teks
Cairncross, Alec
Butterworth, 1960
Buku Teks
Carlson, Valdemar, author
The Blakiston, 1946
Buku Teks
Johnson, Alvin S., author
N.Y. D.C. Hearh & Co., 1911
Buku Teks