@book{69425,
	author = {Ostrom, Elinor},
	title = {Governing the commons  the evolution of institutions for collective action},
	publisher = {Cambridge University Press},
	year = {2008},
	series = {The Political economy of institutions and decisions},
	address = {Cambridge (Inglaterra)},
	url = {http://www.loc.gov/catdir/toc/cam025/90001831.html}
}