@book{22693,
	author = {Verschaffel, Lieven,},
	title = {Words and Worlds :},
	publisher = {Brill | Sense,},
	year = {2009.},
	series = {New Directions in Mathematics and Science Education ;},
	address = {Leiden; },
	url = {http://dx.doi.org/10.1163/9789087909383}
}