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Topology and Set Theory Seminar

Weekly research seminar


Organizers

Information

Wednesdays, 4:15 p.m. , room: 5050

Research fields

List of talks

  • April 26, 2023, 4:15 p.m.
    Jarosław Swaczyna (Lodz University of Technology)
    Continuity of coordinate functionals for ideal Schauder basis
    Given an ideal of subsets of natural numbers I we say that a sequence (x_n) is I-convergent to x if for every ε>0 condition {n \in N:d(x_n,x)>ε}\in I holds. We may use this notion to …

  • April 19, 2023, 4:15 p.m.
    Tomasz Weiss (Cardinal Stefan Wyszyński University in Warsaw)
    Countably perfectly meager and countably perfectly null sets
    We study a strengthening of the notion of a universally meager set and its dual counterpart that strengthens the notion of a universally null set. We say that a subset A of a perfect Polish …

  • March 29, 2023, 4:15 p.m.
    Daria Michalik (University of Warsaw)
    Blocking properties of the diagonal in Cartesian product
    The abstract of the talk can be found on the webpage of our seminar: https://www.mimuw.edu.pl/en/seminaria/topology-and-set-theory-seminar

  • March 22, 2023, 4:15 p.m.
    Taras Banakh (Ivan Franko National University of Lviv and UJK Kielce)
    An example of a 36-Shelah group
    A group $G$ is called $n$-Shelah if $G=A^n$ for any subset $A\subseteq G$ of cardinality $|A|=|G|$. In 1980 Saharon Shelah constructed his famous CH-example of an uncountable 6640-Shelah group. This group was the first example …

  • March 15, 2023, 4:15 p.m.
    Wiesław Kubiś (Akademia Nauk Republiki Czeskiej)
    Ultrametric homogeneous structures
    We shall present the theory of homogeneous Polish ultrametric structures. Our starting point is a Fraı̈ssé class of finite structures and the crucial tool is the universal homogeneous epimorphism. The new Fraı̈ssé limit is an …

  • March 8, 2023, 4:15 p.m.
    Zdeněk Silber (IM PAN)
    Weak* derived sets
    The weak* derived set of a subset A of a dual Banach space X* is the set of weak* limits of bounded nets in A. It is known that a convex subset of a dual …

  • March 1, 2023, 4:15 p.m.
    Adam Kwela (University of Gdańsk)
    Katětov order and its applications
    This talk is an overview of my recent articles on ideals on countable sets. I will present set-theoretic and topological applications of Katětov order on ideals, focusing on distinguishing certain classes of sequentially compact spaces …

  • Jan. 25, 2023, 4:15 p.m.
    Kamil Ryduchowski (Doctoral School of Exact and Natural Sciences UW)
    On antiramsey colorings of uncountable squares and geometry of nonseparable Banach spaces
    A subset Z of a Banach space X is said to be r-equilateral (r-separated) if every two distinct elements of Z are in the distance exactly (at least) r from each other. We will address …

  • Jan. 18, 2023, 4:15 p.m.
    Piotr Szewczak (Cardinal Stefan Wyszyński University in Warsaw)
    Totally imperfect Menger sets: Part 2
    A set of reals X is Menger if for any countable sequence of open covers of X one can pick finitely many elements from every cover in the sequence such that the chosen sets cover …

  • Jan. 11, 2023, 4:15 p.m.
    Piotr Szewczak (Cardinal Stefan Wyszyński University in Warsaw)
    Totally imperfect Menger sets
    A set of reals X is Menger if for any countable sequence of open covers of X one can pick finitely many elements from every cover in the sequence such that the chosen sets cover …

  • Dec. 21, 2022, 4:15 p.m.
    Damian Sobota (Universität Wien, Kurt Gödel Research Center for Mathematical Logic)
    On continuous operators from Banach spaces of Lipschitz functions onto c_0
    During my talk I will discuss some of our recent results concerning the existence of continuous operators from the Banach spaces Lip_0(M) of Lipschitz real-valued functions on metric spaces M onto the Banach space c_0 …

  • Dec. 14, 2022, 4:15 p.m.
    Piotr Koszmider (IM PAN)
    Overcomplete sets
    The density of a topological vector space (tvs) X is the minimal cardinality of a dense subset of X. A subset of a tvs is called linearly dense if the set of all  linear combinations …

  • Dec. 7, 2022, 4:15 p.m.
    Tomasz Kania (Jagiellonian University)
    Renormings of c_0(Γ)
    A biorthogonal system in a Banach space is called Auerbach whenever both the vectors and the associated functionals are precisely of norm 1. We will show that assuming the Continuum Hypothesis, there exist renormings of …

  • Nov. 30, 2022, 4:15 p.m.
    Witold Marciszewski (University of Warsaw)
    On \omega-Corson compact spaces and related classes of Eberlein compacta
    Recall that a compact space K is Eberlein compact if it can be embedded into some Banach space X equipped with the weak topology. A compact space K is \omega-Corson compact if, for some set …

  • Nov. 16, 2022, 4:15 p.m.
    Lyubomyr Zdomskyy (Technische Universität Wien)
    On cardinalities of Lindelöf first countable spaces
    We shall present the main ideas of the construction of a Lindelöf first countable T_1 space of cardinality bigger than continuum. This is a modification of an earlier construction invented by Gorelic. It is well-known …