Ladel, S., & Kortenkamp U.  (2013).  An activity-theoretic approach to multi-touch tools in early maths learning.  The International Journal for Technology in Mathematics Education. 20, 

Ladel, S., & Kortenkamp U.  (2011).  An activity-theoretic approach to multi-touch tools in early maths learning.  Proceedings of ATATEMLO 2011 in Paris.  

Ladel, S., & Kortenkamp U.  (2011).  Finger-Symbol-Sets and Multi-Touch for a better understanding of numbers and operations.  Proceedings of CERME 7, Rzeszow.  

Ladel, S., & Kortenkamp U.  (2011).  Implementation of a multi-touch-environment supporting finger symbol sets.  Proceedings of CERME 7, Rzeszow.  

Ladel, S., & Kortenkamp U.  (2009).  Realisations of MERS (Multiple Extern Representations) and MELRS (Multiple Equivalent Linked Representations) in Elementary Mathematics Software.  (Durand-Guerrier, V., Soury-Lavergne S., & Arzarello F., Ed.).Proceedings of the Sixth Congress of the European Society for Research in Mathematics Education. January 28th - February 1st 2009, Lyon (France).  

Ladel, S., & Kortenkamp U.  (2009).  Virtuell-enaktives Arbeiten mit der ?Kraft der Fünf''.  MNUprimar.