@book{73528,
	author = {Freudenthal, Hans, and ebrary, Inc.},
	title = {Didactical phenomenology of mathematical structures},
	publisher = {Kluwer Academic,},
	year = {1983.},
	address = {Boston :},
	url = {http://site.ebrary.com/lib/rucke/Doc?id=10047060}
}