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Wydział Matematyki, Informatyki i Mechaniki Uniwersytetu Warszawskiego

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Topology and Set Theory Seminar

Weekly research seminar


List of talks

  • 2020-02-26, 16:15, 5050

    Piotr Borodulin-Nadzieja (University of Wrocław)

    Analytic P-ideals and Banach spaces

    I will talk about certain symmetries between analytic P-ideals and Banach spaces with unconditional bases (e.g. I will give some examples of Banach spaces motivated by ideals and vice-versa). I will present a theorem saying that ideals induced by compact families of finite sets are not F_sigma (and ...

  • 2020-01-22, 16:15, 5050

    Adam Kwela (University of Gdańsk)

    Haar-smallest sets

    We will be interested in the following notions of smallness: a subset A of an abelian Polish group X is called Haar-countable/Haar-finite/Haar-n if there are a Borel set B containing A and a copy C of the Cantor set in X such that (C+x)\cap B is countable/finite/of cardinality at most n, for all...

  • 2020-01-15, 16:15, 5050

    Michael Levin (Ben-Gurion University of the Negev, Israel)

    Light maps of compacta

    Based on a result of H. Torunczyk, R. Pol showed that a light map f: X->Y  from a compactum X with dim X > 2 to a finite dimensional compactum Y is injective on a non-trivial subcontinuum of X.  Pol also showed that in the above statement the restriction dim X > 2 is necessary a...

  • 2020-01-08, 16:15, 5050

    Witold Marciszewski (University of Warsaw)

    Countable dense homogeneous linear topological spaces

    Recall that a topological space X is countable dense homogeneous (CDH) if X is separable, and given countable dense subsets D,E of X, there is an autohomeomorphism of X mapping D onto E. This is a classical notion tracing back to works of Cantor, Frechet and Brouwer. The canonical examples of CDH sp...

  • 2019-12-18, 16:15, 5050

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

    Convergence of measures in the random model

    A Boolean algebra B has the Vitali--Hahn--Saks property if every sequence of measures on B which converges to 0 on elements of B converges also to 0 on every Borel subset of the Stone space of B. Examples of Boolean algebras having the property include e.g. sigma-complete ones. Some time ago we show...

  • 2019-12-11, 16:15, 5050

    Piotr Szewczak (Cardinal Wyszyński University in Warsaw)

    Null-additive sets and the property gamma

    A subset X of the real line is null-additive if for each null set Y, the set X+Y is null. Under Martin Axiom, Galvin nad Miller constructed an uncountable null-additive set whose continuous images are also null-additive; this set has the property gamma, a strong combinatorial covering property. Bart...

  • 2019-12-04, 16:15, 5050

    Szymon Głąb (Institute of Mathematics Technical University of Łódź)

    Inverse limits of finite graphs (joint project with Stefan Geschke and Wiesław Kubiś)

    The random graph R is the unique countable graph which contains isomorphic copies of all countable graphs and is homogeneous in the sense that every isomorphism between its finite subgraphs extends to an automorphism of R. Actually, the existence, universality and uniqueness of the random graph foll...

  • 2019-11-27, 16:15, 5050

    Grzegorz Plebanek (University of Wrocław)

    Monolithic spaces of measures

    For a compact space K, we consider the space P(K) of regular probability measures on K, equipped with the weak* topology. For zerodimensional spaces K, we can, equvalently, speak of  P(A), the space of finitely additive measures on a Boolean algebra A (with the topology of converence on element...

  • 2019-11-06, 16:15, 5050

    Piotr Zakrzewski (University of Warsaw)

    On Mazurkiewicz's sets and regularity properties of sigma-ideals

    The talk will present results from a joint paper with Roman Pol. Let f:X --> Y be a continuous surjection of the compact metrizable space X onto an uncountable compact metrizable space Y. A Mazurkiewicz set for f is a G_{delta sigma}-set M in X which is a partial selector for f and each G_de...

  • 2019-10-31, 16:15, 5050

    Arturo Antonio Martínez Celis Rodríguez (IMPAN)

    Cardinal Invariants and Rosenthal families

    Rosenthal's lemma is a classical result that concerns sequences of measures on pairwise disjoint sets and a Rosenthal family is a collection of infinite subsets of the natural numbers that can replace the collection of all infinite subsets of natural numbers in Rosenthal's lemma. In this talk we wil...

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