*Ladel, S. & Kortenkamp, U. (2011): Finger-symbol-sets and multi-touch for a better understanding of numbers and operations. In: Proceedings of CERME 7, Rzeszów. 2011 | *Ladel, S. & Kortenkamp, U. (2011): Finger-symbol-sets and multi-touch for a better understanding of numbers and operations. In: Proceedings of CERME 7, Rzeszów. 2011 |