P. Frymier, R. Ford, H. Berg, und P. Cummings. Proceedings of the National Academy of Sciences of the United States of America, 92 (13):
6195-6199(Juni 1995)
J. Wang, und N. Parameswaran. Proceedings of the Pan-Sydney area workshop on Visual information processing, Seite 87--90. Darlinghurst, Australia, Australia, Australian Computer Society, Inc., (2004)