F. Arzarello. the 24th Conference of the International Group for the Psychology of Mathematics Education (PME), 1, page 23--38. Hiroshima, Japan, (2000)
C. Sackur, T. Assude, and M. Maurel. European Research in Mathematics Education I.I + I.II Proceedings of the First Conference of the European Society for Research in Mathematics Education, 1 & 2, Osnabrueck, Forschungsinstitut fuer Mathematikdidaktik, (1999)