, 2005, Notes on a semiotically inspired theory of teaching and learning, in M. H. G. . Hoffmann, J. Lenhard & F. Seeger (eds.), Activity and sign, Dordrecht, Springer, pp. 67-76.
with Hoffmann, M. H. , Lenhard, J. (eds) , 2005a, Activity and sign: grounding mathematics education, Springer, Dordrecht.