Teppo, A., Speiser, R., Søndergaard, B. D. & van den Heuvel-Panhuizen, M. (2004). Keeping the mathematics in mathematics education research. I M. Johnsen Høines & A. B. Fuglsang (red.), Proceedingf of the 28th conference of the International Group for the Psychology of Mathematics Education, PME28, Bergen, Norway, July 14-18 2004. Bergen: Bergen University College (Bind 1, s. 261). <Forlag uden navn>.