1. Chellas B.F., Modal Logic: An Introduction. Cambridge University Press, 1980.
2. Dubois D. and Prade H., Possibility Theory.Plemun Press, 1988.
3. Dubois D. and Prade H., Conditional objects, possibility theory and default rules. In G.Crocco, L.Farinas del Cerro, and A.Herzig, Conditionals: from Philosophy to Computer Science, Studies in Logic and Computation 5, pp. 301–336, 1995.
4. Harmanec D., Klir G.J. and Resconi G., “On Modal Logic Interpretation of Dempster-Shafer Theory of Evidence”. Int. J. Intelligent Systems, vol. 9, pp. 941–951, 1994.
5. Hughes G.E. and Cresswell M.J., An Introduction to Modal Logic.Methuen, 1968.