1. Hegel GWF . Philosophy of History. New York: Collier, 1905.
2. Lombardi R . Visual perception and denture esthetics. J Prosthet Dent, 1973; 29: 352–382.
3. Plato . Republic. c 400 BC
4. Ehrenzweig A . The Hidden Order of Art. Berkley: University of California Press, 1971
5. Ahmad I . Digital and Conventional Photography: A Practical Clinical Manual. Chicago: Quintessence Publishing, 2004 (in print).