B. Schwarz, T. Dreyfus, N. Hadas, and R. Hershkowitz. the 28th international conference for the psychology of mathematics education, 4, Bergen, Norway, Bergen University College., (2004)
A. Maclean, R. Young, and T. Moran. CHI '89: Proceedings of the SIGCHI conference on Human factors in computing systems, page 247--252. New York, NY, USA, ACM Press, (1989)