@inbook {805,
	title = {Artifact-Centric Activity Theory - A Framework for the Analysis of the Design and Use of Virtual Manipulatives},
	booktitle = {International Perspectives on Teaching and Learning Mathematics with Virtual Manipulatives},
	year = {2016},
	pages = {25-40},
	publisher = {Springer Verlag},
	organization = {Springer Verlag},
	address = {Heidelberg},
	author = {Ladel, Silke and Kortenkamp, Ulrich},
	editor = {Moyer-Packenham, Patricia}
}
