@conference {765,
	title = {Flexible Use and Understanding of Place Value Via Traditional and Digital Tools. Research Report.},
	booktitle = {Proceedings of the 38th Conference of the International Group for the Psychology of Mathematics Education and the 36th Conference of the North American Chapter of the Psychology of Mathematics Education},
	year = {2014},
	publisher = {Psychology of Mathematics Education (PME)},
	organization = {Psychology of Mathematics Education (PME)},
	address = {Vancouver, Canada},
	author = {Kortenkamp, Ulrich and Ladel, Silke},
	editor = {Lilijedahl, Peter and Nicol, Cynthia and Oesterle, Susan and Allan, Darien}
}
@conference {754,
	title = {Finger-symbol-sets and multi-touch for a better understanding of numbers and operations},
	booktitle = {Proceedings of the Seventh Congress of the European Society for Research in Mathematics Education.},
	year = {2011},
	month = {Februar},
	publisher = {Congress of the European Society for Research in Mathematics Education (CERME)},
	organization = {Congress of the European Society for Research in Mathematics Education (CERME)},
	address = {Rzesz{\'o}w, Poland},
	author = {Ladel, Silke and Kortenkamp, Ulrich},
	editor = {Pytlak, Marta and Rowland, Tim and Swoboda, Ewa}
}
