@book{59167,
	author = {Benthem, J. F. A. K. van},
	title = {Handbook of modal logic},
	publisher = {Elsevier},
	year = {2007},
	series = {Studies in logic and practical reasoning},
	address = {Ámsterdam (Holanda)},
	url = {http://www.loc.gov/catdir/enhancements/fy0665/2006050759-d.html}
}