Organizers

prof. dr hab. Witold Marciszewski
prof. dr hab. Piotr Zakrzewski

Information

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

Research fields

Topology and Set Theory

List of talks

Nov. 29, 2023, 4:15 p.m.
Maciej Malicki (IM PAN)
Compacta and their homeomorphism groups from posets
Very recently A. Bartoš, T. Bice and A. Vignati discovered a duality, generalizing the Stone duality, between second countable T_1 compacta and graded omega-posets. Their approach allows for elementary combinatorial constructions, in the spirit of …
Nov. 22, 2023, 4:15 p.m.
Jindrich Zapletal (University of Florida)
Fraenkel-Mostowski models revisited
A dynamical ideal is a group G acting on a set X, together with an ideal I on X invariant under the action. A dynamical ideal comes with an associated model of ZF set theory. …
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Nov. 8, 2023, 4:15 p.m.
David Chodounsky (Institute of Mathematics of the Czech Academy of Sciences)
Games for chromatic numbers of analytic graphs
We define games which characterize countable coloring numbers of analytic graphs on Polish spaces. These games can provide simple verification of the countable chromatic number of certain graphs. We also get a simpler proof of …
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Oct. 25, 2023, 4:15 p.m.
Tomasz Kochanek (University of Warsaw)
Operator semigroups in the Calkin algebra, part 2
The abstract of the talk can be found here: https://drive.google.com/file/d/1xCTvKwjFXONxqUN1NurltvhGewn6GyV7/view?usp=sharing
- abstract, part 2
Oct. 18, 2023, 4:15 p.m.
Tomasz Kochanek (University of Warsaw)
Operator semigroups in the Calkin algebra
The abstract of the talk can be found here: https://drive.google.com/file/d/1aMk2GrPJTYMP8PiMOKgJU4Hay5186G5s/view?usp=sharing
- abstract
Oct. 11, 2023, 4:15 p.m.
Jesús M. F. Castillo (Universidad de Extremadura)
K)-space scrapboo
- file
June 14, 2023, 4:15 p.m.
Jakub Andruszkiewicz (Doctoral School of Exact and Natural Sciences UW)
Cofinalities of the symmetric group and of the ultrapowers of ω
We consider the following cardinal invariants of the continuum: cf(Sym(ω)), being the cofinality of the group of permutations of ω, and mcf, defined as the minimal cofinality of an ultrapower of ω over any non-principal …
May 31, 2023, 4:15 p.m.
Piotr Koszmider (IM PAN)
Ramsey properties of the distance on nonseparable spheres
Given a nonseparable metric space (M,d) bounded by 2 we consider (A) dichotomies D_r for r in (0,2): either there is uncountable subset N of M such that d(x, y) > r for all distinct …
May 24, 2023, 4:15 p.m.
Grzegorz Plebanek (University of Wrocław)
Countable discrete extensions of compact lines
We consider a separable compact line K and its extension L consisting of K and a countable number of isolated points. The main object of study is the existence of a bounded extension operator E: …
May 10, 2023, 4:15 p.m.
Aristotelis Panagiotopoulos (Carnegie Mellon University)
Menger continua via projective Fraïssé theory
Projective Fraïssé theory was introduced by T.Irwin and S.Solecki as a natural framework for analyzing the dynamics of homeomorphism groups of compact metrizable spaces in terms of finite combinatorics. In this talk I will provide …
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
- abstract
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 …