Ladel, S., & Kortenkamp, U..  (2011).  Implementation of a multi-touch-environment supporting finger-symbol-sets. In M.  Pytlak, Rowland, T., & Swoboda, E. (Hrsg.), Proceedings of the Seventh Congress of the European Society for Research in Mathematics Education.. gehalten auf der Februar, Rzeszów, Poland: Congress of the European Society for Research in Mathematics Education (CERME).