Psycharis, G. (2013). Abstraction through instrumentalization. In A. M. Lindmeier & Heinze, A. (Eds.), Proceedings of the 37th Conference of the International Group for the Psychology of Mathematics Education (PME 37), Research forum “Activity theoretical approaches to mathematics classroom practices with the use of technology” (Vol. 1, pp. 192-196). Kiel, Germany: PME.