@book{126145,
	author = {Chellas, Brian F.},
	title = {Modal logic :},
	publisher = {Cambridge University Press,},
	year = {[1980]},
	address = {Cambridge [Eng.] ;},
	note = {Includes indexes.},
	url = {http://www.loc.gov/catdir/description/cam022/76047197.html}
}