@book{512,
	author = {Mason, John, and Graham, Alan,},
	title = {Developing thinking in algebra /},
	publisher = {Open University in association with Paul Chapman Pub. ;},
	year = {2005.},
	address = {London :},
	url = {http://www.loc.gov/catdir/enhancements/fy0659/2004117187-d.html}
}