1. Vernon, P. E., ed. 1970.Creativity, 55Har‐mondsworth: Penguin Books.
2. Hadamard, Jacques. 1949.The Psychology of Invention in the Mathematical Field, 15Princeton: Princeton University Press.
3. Krebs, H. A. and Shelley, J. H., eds. 1975.The Creative Process in Science and Medicine, 31Amsterdam: Exerpta Medica.