Yu, Francis T.S., author
John Wiley & Sons, 1983
Buku Teks
Pirenne, Henri, author
Dover, 2001
Buku Teks
Albrecht, Leon K., author
Macmillan, 1973
Buku Teks
Rosenberg, Jerry M., author
John Wiley & Sons, 1987
Buku Referensi
Casady, Mona J. author
South-Western Publishing, 1985
Buku Teks