1. Dempster, A.P.: Upper and lower probabilities induced by a multivalued mapping. Ann. Probability 38, 325–339 (1967)
2. Dubois, D., Prade, H.: A set-theoretic view of belief functions: logical operations and approximations by fuzzy sets. Intern. J. General Systems 12, 193–226 (1986)
3. Gierz, G., Hofman, K.H., Keimel, K., Lawson, J.D., Mislove, M., Scott, D.S.: A Compendium of Continuous Lattices. Springer (1980)
4. Goodman, I.R.: Fuzzy sets as equivalence classes of random sets. In: Yager, R. (ed.) Fuzzy Sets and Possibility Theory, pp. 327–343 (1982)
5. Hajek, K.: Sampling from a Finite Population. Marcel Dekker, New York (1981)