Weekly research seminar
Organizers
 prof. dr hab. Witold Marciszewski
 prof. dr hab. Piotr Zakrzewski
Information
Wednesdays, 4:15 p.m. , room: 5050Research fields
List of talks

March 22, 2023, 4:15 p.m.
Taras Banakh (Ivan Franko National University of Lviv and UJK Kielce)
An example of a 36Shelah 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 CHexample of an uncountable 6640Shelah 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 settheoretic 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 requilateral (rseparated) 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 realvalued 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 \omegaCorson 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 \omegaCorson 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 wellknown …

Nov. 9, 2022, 4:15 p.m.
Mikołaj Krupski (University of Warsaw)
\kappapseudocompactness and uniform homeomorphisms of function spaces
A Tychonoff space X is called \kappapseudocompact if for every continuous mapping f of X into R^\kappa the image f(X) is compact. This notion generalizes pseudocompactness and gives a stratification of spaces lying between pseudocompact …

Oct. 26, 2022, 4:15 p.m.
Maciej Malicki (IM PAN)
Isomorphism of locally compact Polish metric structures
Gao and Kechris asked if the isometry relation on the space of locally compact Polish metric spaces is (Borel) reducible to the isomorphism relation of countable graphs. It turns out that this question is easier …

Oct. 19, 2022, 4:15 p.m.
Paweł Krupski (Wrocław University of Science and Technology)
On the hyperspace of simple closed curves in the plane
The Vietoris hyperspace of simple closed curves in the plane will be discussed. Its characterization is a challenging open problem. An elementary proof of the hyperspace's local contractibility will be presented. Joint work with Krzysztof Omiljanowski.  …