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Wydział Matematyki, Informatyki i Mechaniki Uniwersytetu Warszawskiego

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Seminarium „Topologia i teoria mnogości”

Cotygodniowe seminarium badawcze


Lista referatów

  • 2019-10-23, godz. 16:15, 5050

    Roman Pol (University of Warsaw)

    On uniformly tight sets of probability measures on the rationals

    The talk will present results obtained jointly with Piotr Zakrzewski.   Let P(Q) be the space of probability measures on the rationals Q, equipped with the weak topology. A set A in P(Q) is uniformly tight if for any r > 0 there is a compact set C in Q such that u(C) > 1 - r for ever...

  • 2019-10-16, godz. 16:15, 5050

    Mikołaj Krupski (University of Warsaw)

    Hereditarily Baire hyperspaces, filters and spaces of measures - part 2

    This part does not depend on the material presented under the same title during the first part of the talk. A topological space X is Baire if the intersection of a countable family of open dense sets in X is dense. We say that X is hereditarily Baire if every closed subspace of X is Baire. It wa...

  • 2019-10-09, godz. 16:15, 5050

    Mikołaj Krupski (University of Warsaw)

    Hereditarily Baire hyperspaces, filters and spaces of measures

    A topological space X is Baire if the intersection of a countable family of open dense sets in X is dense. We say that X is hereditarily Baire if every closed subspace of X is Baire. It was observed by the speaker that hereditary Baireness of the hyperspace of all nonempty compact subsets of a s...

  • 2019-06-12, godz. 16:15, 5050

    Mikołaj Krupski (University of Warsaw)

    Embedding of the Free Abelian Topological Group A(X x X) into A(X)

    In my talk I will discuss the following question: For which separable metrizable spaces X does the free abelian topological group A(X x X) isomorphically embed into A(X)? While for many natural spaces X such an embedding exist, I will show that there is a compact metric space X (Cook continuum) su...

  • 2019-06-05, godz. 16:15, 5050

    Piotr Koszmider (IMPAN)

    On R-embeddability of almost disjoint families and some problems concerning C*-algebras

    An almost disjoint family A of subsets of N is said to be R-embeddable if there is a function f:N→R such that the sets f[A] are ranges of real sequences converging to distinct reals for distinct A∈A. It is well known that almost disjoint families which have few separations, such as Luzin familie...

  • 2019-05-29, godz. 16:15, 5050

    Tomasz Weiss (Cardinal Wyszyński University in Warsaw)

    Some properties of the * operation on families of special subsets of R. Algebraic sum of a perfect set and large subsets of R

    In the first part of this talk I will present the following lemma. Assume CH. Given a non trivial ideal F of subsets of R which is Borel supported, translation invariant, with cov(F) =c/the continuum/ and a set A which does not belong to F, there is an X such that for every Y from F , X+Y is not eq...

  • 2019-05-22, godz. 16:15, 5050

    Tomasz Cieśla (McGill University)

    Measurable Hall's theorem for actions of abelian groups

    We prove a measurable version of the Hall marriage theorem for actions of finitely generated abelian groups. In particular, it implies that for free measure-preserving actions of such groups, if two equidistributed measurable sets are equidecomposable, then they are equidecomposable usin...

  • 2019-05-15, godz. 16:15, 5050

    Witold Marciszewski (University of Warsaw)

    Twist and Shout - a continuation

    We consider the class of Banach spaces Y for which the space c_0 admits a nontrivial twisted sum with Y, i.e., there exists a Banach space X containing a noncomplemented copy Z of c_0 such that the quotient space X/Z is isomorphic to Y. We present a characterization of such spaces Y in terms of prop...

  • 2019-05-08, godz. 16:15, 5050

    Witold Marciszewski (University of Warsaw)

    Twist and Shout

    We consider the class of Banach spaces Y for which the space c_0 admits a nontrivial twisted sum with Y, i.e., there exists a Banach space X containing a noncomplemented copy Z of c_0 such that the quotient space X/Z is isomorphic to Y. We present a characterization of such spaces Y in terms of pro...

  • 2019-04-17, godz. 16:15, 5050

    Damian Sobota (Kurt Gödel Research Center, University of Vienna)

    Selected topics in convergence of measures on compact spaces

    During my talk I'll present some most recent results of my joint work with Lyubomyr Zdomskyy concerning different aspects of convergence of sequences of Radon measures on compact spaces. Among others, I'll present a (sketch of a) constructive and elementary proof of the fact that the Banach spac...

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