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A criterion for local resolvability of a space and the ω-problem

100%

Ponomarev S. P.

Journal of Applied Analysis

2007

tom Vol. 13, nr 1

83-96

The notion of the resolvability of a topological space was introduced by E. Hewitt [8]. Recently it was understood that this notion is also important in the study of ω)-primitives, especially in the case of nonmetrizable spaces. In the present paper a criterion for the resolvability of a topological space at a point ("local resolvability") is given. This criterion, stated in terms of oscillation and quasicontinuity, permits to conclude, for instance, that on irresolvable spaces no positive continuous real-valued function has an ω-primitive. The result is strenghtened in the case of SI-spaces. It is also shown that every non- negative upper semicontinuous function on a resolvable Baire space has an ω)-primitive.

Countable compact scattered T2 spaces and weak forms of AC

70%

Keremedis K. , Felouzis E. , Tachtsis E.

Bulletin of the Polish Academy of Sciences. Mathematics

2006

tom Vol. 54, no 1

75-84

We show that: (1) It is provable in ZF (i.e., Zermelo-Fraenkel set theory minus the Axiom of Choice AC) that every compact scattered T2 topological space is zero-dimensional. (2) If every countable union of countable sets of reals is countable, then a countable compact T2 space is scattered iff it is metrizable. (3) If the real line R can be expressed as a well-ordered union of well-orderable sets, then every countable compact zero-dimensional T2 space is scattered. (4) It is not provable in ZF+¬AC that there exists a countable compact T2 space which is dense-in-itself.