1. Bull, R. A., and K. Segerberg, 1984, ?Basic modal logic?, In Gabbay, D. and Guenthner, F., eds.: Handbook of philosophical logic, Vol. II: Extensions of classical logic, Dordrecht, 1?88.
2. Goré, R., 1992, ?Cut-free sequent and tableau systems for prepositional normal modal logics?, Cambridge computer laboratory technical report Nr. 257, Cambridge.
3. Goré, R., 1994, ?Cut-free sequent and tableau systems for propositional Diodorean modal logics?, Studia Logica 53, 433?457.
4. Goré, R., 1994, ?Semi-analytic tableaux for propositional normal modal logics with applications to nonmonotonicity?, Logique et Analyse, 133?134.
5. Hughes, G. E., and M. J. Cresswell, 1984, A companion to modal logic, London.