Gray, D.
Pergamon Press, 1966
Buku Teks
Edwards, Harry J., author
McGraw-Hill, 1980
Buku Teks
Letherman, K.M., author
Pergamon Press, 1981
Buku Teks
Harbron, John D.
FRederick A. Praeger, 1963
Buku Teks
Gray, Christine D.
Clarendon Press, 1987
Buku Teks