Zagoria, Donald S.
Princeton University press, 1962
Buku Teks
Matthews, Donald R.
The University of North Carolina Press, 1960
Buku Teks
R. Conquest
Macmillan & CO LTD, 1960
Buku Teks
McGraw-Hill, 1955
Buku Referensi
Askeland, Donald R.
Chapman & Hall, 1990
Buku Teks