@book {758, title = {Early Mathematics Learning. Selected Papers of the POEM 2012 Conference.}, year = {2013}, publisher = {Springer}, organization = {Springer}, address = {New York}, editor = {Kortenkamp, Ulrich and Brandt, Birgit and Benz, Christiane and Krummheuer, G{\"o}tz and Ladel, Silke and Vogel, Rose} } @inbook {760, title = {Number Concepts - Process of Internalization and Externalization by the Use of Multi-Touch Technology}, booktitle = {Early Mathematics Learning. Selected Papers of the POEM 2012 Conference.}, year = {2013}, pages = {237-253}, publisher = {Springer}, organization = {Springer}, address = {New York}, author = {Ladel, Silke and Kortenkamp, Ulrich}, editor = {Kortenkamp, Ulrich and Brandt, Birgit and Benz, Christiane and Krummheuer, G{\"o}tz and Ladel, Silke and Vogel, Rose} }