[1] W. W. Comfort S. Negrepontis:
The theory of ultrafilters. Springer-Verlag, New York--Heidelberg, 1974.
MR 0396267
[3] M. Katětov:
Quasi-entropy of finite weighted metric spaces. Comment. Math. Univ. Carolinae 17 (1976), 777-806.
MR 0434618
[4] M. Katětov:
Extensions of the Shannon entropy to semimetrized measure spaces. Comment. Math. Univ. Carolinae 21 (1980), 171-192.
MR 0566249
[5] M. Katětov:
Extended Shannon entropies I. Czechosl. Math. J. 33 (108) (1983), 564-601.
MR 0721088