Kirgis, Frederic L.
West Publishing, 1993
Buku Teks
Okolie, Charles Chukwuma
Frederick A. Praeger, 1975
Buku Teks
edited by Julio Faundez
St. Martin's Press, 1997
Buku Teks
Benham, Frederic
Oxford University Press, 1962
Buku Teks
edited by Evan Luard
Praeger, 1966
Buku Teks