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Approximating Radon measures on first-countable compact spaces

Grzegorz Plebanek — 2000

Colloquium Mathematicae

The assertion every Radon measure defined on a first-countable compact space is uniformly regular is shown to be relatively consistent. We prove an analogous result on the existence of uniformly distributed sequences in compact spaces of small character. We also present two related examples constructed under CH.

On Pettis integral and Radon measures

Grzegorz Plebanek — 1998

Fundamenta Mathematicae

Assuming the continuum hypothesis, we construct a universally weakly measurable function from [0,1] into a dual of some weakly compactly generated Banach space, which is not Pettis integrable. This (partially) solves a problem posed by Riddle, Saab and Uhl [13]. We prove two results related to Pettis integration in dual Banach spaces. We also contribute to the problem whether it is consistent that every bounded function which is weakly measurable with respect to some Radon measure is Pettis integrable....

Nonseparable Radon measures and small compact spaces

Grzegorz Plebanek — 1997

Fundamenta Mathematicae

We investigate the problem if every compact space K carrying a Radon measure of Maharam type κ can be continuously mapped onto the Tikhonov cube [ 0 , 1 ] κ (κ being an uncountable cardinal). We show that for κ ≥ cf(κ) ≥ κ this holds if and only if κ is a precaliber of measure algebras. Assuming that there is a family of ω 1 null sets in 2 ω 1 such that every perfect set meets one of them, we construct a compact space showing that the answer to the above problem is “no” for κ = ω. We also give alternative proofs...

On Pettis integrals with separable range

Grzegorz Plebanek — 1993

Colloquium Mathematicae

Several techniques have been developed to study Pettis integrability of weakly measurable functions with values in Banach spaces. As shown by M. Talagrand [Ta], it is fruitful to regard a weakly measurable mapping as a pointwise compact set of measurable functions - its Pettis integrability is then a purely measure-theoretic question of an appropriate continuity of a measure. On the other hand, properties of weakly measurable functions can be translated into the language of topological measure theory...

On positive embeddings of C(K) spaces

Grzegorz Plebanek — 2013

Studia Mathematica

We investigate isomorphic embeddings T: C(K) → C(L) between Banach spaces of continuous functions. We show that if such an embedding T is a positive operator then K is the image of L under an upper semicontinuous set-function having finite values. Moreover we show that K has a π-base of sets whose closures are continuous images of compact subspaces of L. Our results imply in particular that if C(K) can be positively embedded into C(L) then some topological properties of L, such as countable...

Convex Corson compacta and Radon measures

Grzegorz Plebanek — 2002

Fundamenta Mathematicae

Assuming the continuum hypothesis, we show that (i) there is a compact convex subset L of Σ ( ω ) , and a probability Radon measure on L which has no separable support; (ii) there is a Corson compact space K, and a convex weak*-compact set M of Radon probability measures on K which has no G δ -points.

Countable tightness in the spaces of regular probability measures

Grzegorz PlebanekDamian Sobota — 2015

Fundamenta Mathematicae

We prove that if K is a compact space and the space P(K × K) of regular probability measures on K × K has countable tightness in its weak* topology, then L₁(μ) is separable for every μ ∈ P(K). It has been known that such a result is a consequence of Martin's axiom MA(ω₁). Our theorem has several consequences; in particular, it generalizes a theorem due to Bourgain and Todorčević on measures on Rosenthal compacta.

On sequential properties of Banach spaces, spaces of measures and densities

Piotr Borodulin-NadziejaGrzegorz Plebanek — 2010

Czechoslovak Mathematical Journal

We show that a conjunction of Mazur and Gelfand-Phillips properties of a Banach space E can be naturally expressed in terms of * continuity of seminorms on the unit ball of E * . We attempt to carry out a construction of a Banach space of the form C ( K ) which has the Mazur property but does not have the Gelfand-Phillips property. For this purpose we analyze the compact spaces on which all regular measures lie in the * sequential closure of atomic measures, and the set-theoretic properties of generalized...

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