Arrow, Kenneth J., author
Holden-Day, 1971
Buku Teks
Downie, Jack
Gerald Duckworth & Co. Ltd, 1958
Buku Teks
Porter, Michael E., author
The Free Press , 1990
Buku Teks
Gray, Edmund R., author
Macmillan, 1990
Buku Teks
Robinson, E. A. G., author
James Nisbet and Co.Ltd., 1958
Buku Teks