@book{20973,
	author = {Liu, Sifeng  and Yi Lin Forrest, Jeffrey },
	title = {Grey Systems},
	publisher = {Springer Berlin Heidelberg},
	year = {2011},
	series = {Understanding Complex Systems},
	address = {Heidelberg, Berlin},
	url = {http://doi.org/10.1007/978-3-642-16158-2}
}