Armstrong, M.A.
Springer-Verlag , 1983
Buku Teks
Foulds, L.R.
New York Springer-Verlag 1984,
Buku Referensi
Greenhood, David
The University of Chicago Press, 1964
Buku Teks
Dupee, F.W., author
Doubleday, 1956
Buku Teks
Swan, Michael, author
Longmans, 1950
Buku Teks