M. Scaife, Y. Rogers, F. Aldrich, and M. Davies. CHI '97: Proceedings of the SIGCHI conference on Human factors in computing systems, page 343-350. New York, NY, USA, ACM Press, (1997)
M. Cerulli, A. Chioccariello, and E. Lemut. 5th CERME conference - congress of European Society for Research in Mathematics Education, Larnaca, Cyprus, (2007)
M. Cerulli, A. Chioccariello, and E. Lemut. Proceedings of the Fourth Congress of the European Society for Research in Mathematics Education (CERME 4), page 591-600. Sant Feliu de Guíxols, Spain,, (2005)