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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

  • 2022-01-12, godz. 16:15, 4420

    Maciej Malicki (IMPAN)

    Large conjugacy classes and weak amalgamation

    Ivanov, and later Kechris and Rosendal, characterized the existence of dense or comeager (diagonal) conjugacy classes in automorphism groups of certain classes of Fraïssé limits. I will show how these results can be extended to limits of weak Fraïssé classes, using an approac...

  • 2021-12-15, godz. 16:15, Zoom

    Sławomir Solecki (Cornell University)

    Closed groups generated by generic measure preserving transformations

    The behavior of a measure preserving transformation, even a generic one, is highly nonuniform. In contrast to this observation, a different picture of a very uniform behavior of the closed group generated by a generic measure preserving transformation T has emerged. This picture included substantial...

    Slides

  • 2021-12-08, godz. 16:15, Zoom

    Paul Szeptycki (York University)

    On a topological Ramsey theorem

    This is joint work with Wiesław Kubiś. We introduce natural strengthenings of sequential compactness called the $r$-Ramsey property for each natural number $r\geq 1$.  We prove that metrizable compact spaces are $r$-Ramsey for all $r$ and give examples of compact spaces that are $r$-Ramsey bu...

    slides

  • 2021-12-01, godz. 16:15, Zoom

    Piotr Szewczak (Cardinal Stefan Wyszyński University in Warsaw)

    Products of Hurewicz, Menger and Lindelof spaces - a continuation

    We consider products of general topological spaces with Hurewicz’s, Menger’s and Lindelof’s covering properties. Assuming the Continuum Hypothesis, we prove that every productively Lindelof space is productively Menger, and every productively Menger space is productively Hurewicz. ...

    slides

  • 2021-11-24, godz. 16:15, Zoom

    Alberto Salguero Alarcón (Universidad de Extremadura, Badajoz, Spain)

    To be a C(K)-space is not a three-space property

    In the setting of Banach spaces, a property P is said to be a three-space property if whenever a Banach space X has a subspace Y so that both Y and the quotient space X/Y satisfy P, then X also satisfies P. It has been known for some time that ``to be isomorphic to a space of continuous functions C(...

    slides

  • 2021-11-17, godz. 16:15, Zoom

    Jan van Mill (University of Amsterdam)

    Universal autohomeomorphisms of $N^*$

    This is joint work with Klaas Pieter Hart. We study the existence of universal autohomeomorphisms of $N^*$. We prove that CH implies there is such an autohomeomorphism and show that there are none in any model where all autohomeomorphisms of $N^*$ are trivial. ...

    slides

  • 2021-11-03, godz. 16:15, 4420

    Piotr Szewczak (Cardinal Stefan Wyszyński University in Warsaw)

    Products of Hurewicz, Menger and Lindelof spaces

    We consider products of general topological spaces with Hurewicz’s, Menger’s and Lindelof’s covering properties. Assuming the Continuum Hypothesis, we prove that every productively Lindelof space is productively Menger, and every productively Menger space is productively Hurewicz. ...

  • 2021-10-27, godz. 16:15, 4420

    Grzegorz Plebanek (University of Wrocław)

    On kappa-Corson compacta

    A compact space is `Corson compact' if it can be embedded into some product of real lines in such a way that the support of every element is countable; kappa-Corson compactness is defined in the same manner, replacing `countable' by `of size < kappa'. That class of kappa-Corson compac...

  • 2021-10-20, godz. 16:15, Zoom

    Jacek Tryba (University of Gdańsk)

    Different kinds of density ideals

    We consider several kinds of ideals described by some densities. We present connections between Erdos-Ulam, density, matrix summability and generalized density ideals and show that a certain inaccuracy in Farah's definition of density ideals leads to Farah's characterization when density ide...

  • 2021-10-13, godz. 16:15, 4420

    Tomasz Weiss (Cardinal Wyszyński University in Warsaw)

    On the algebraic sum of a perfect set and a large subset of the reals

    In M. Kysiak’s paper "Nonmeasurable algebraic sums of sets of reals", (Coll. Math., Vol. 102, No 1, 2005), the following two questions appeared. Assume that A ⊆ R is a non-meager set with the Baire property and P is perfect. Do there exist meager sets X ⊆ A and Y ⊆ P s...

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