Modal logic : an introduction / Brian F. Chellas. Chellas, Brian F. Modality (Logic) BC199.M6 C47 160 CHM Includes indexes. Bibliography: p. [278]-279. Cambridge [Eng.] ; New York : Cambridge University Press, [1980] [1980] 1980 Text xii, 295 p. : http://www.loc.gov/catdir/description/cam022/76047197.html http://www.loc.gov/catdir/toc/cam028/76047197.html eng