Organizers

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

Information

Wednesdays, 4:15 p.m. , room: 4050

Research fields

Topology and Set Theory

List of talks

April 29, 2026, 4:15 p.m.
Maciej Korpalski (University of Wrocław)
Semadeni-Pełczyński derivative and Banach spaces of continuous functions on nonmetrizable cubes
We study Banach spaces C(K) of real-valued continuous functions on finite products of compact lines. It turns out that the topological character of these compact lines can be used to distinguish whether two spaces of …
April 22, 2026, 4:15 p.m.
Julia Ścisłowska (Doctoral School of Exact and Natural Sciences UW)
Modern methods of constructing the Knaster continuum
During my talk I will discuss and compare modern limit-like constructions of building compacta: projective Fraïssé limits and the spectrum of an ω-poset. Those tools can be used to study interesting properties of topological spaces …
April 15, 2026, 4:15 p.m.
Kacper Kucharski (Doctoral School of Exact and Natural Sciences UW)
Function spaces on separable compact lines
A compact line is any linearly ordered compact topological space. During the talk we will provide a complete isomorphism classification of the spaces of real-valued continuous functions endowed with the topology of pointwise convergence $C_p(K)$ …
April 8, 2026, 4:15 p.m.
Mustafa Gülfırat (Ankara University)
Generalized Limits and Ideal Convergence
Let $\mathcal{I}$ be an ideal on $\mathbb{N}$, the set of positive integers. Consider the Banach space $m$ of all real bounded sequences $x$ with $\|x\| = \sup_{k}|x_k|$. A positive linear functional $L$ on $m$ is …
March 25, 2026, 4:15 p.m.
Ruiyuan Chen (University of Warsaw)
Orbitwise topologies and quasi-Polish techniques for Polish group actions
March 18, 2026, 4:15 p.m.
Piotr Koszmider (IM PAN)
Banach spaces of continuous functions on ladder system spaces
For every infinite cardinal kappa there are many known constructions of families of cardinality 2^kappa of pairwise nonhomeomorphic compact Hausdorff spaces of weight kappa. However, the Banach spaces C(K) and C(L) of all continuous real-valued …
March 11, 2026, 4:15 p.m.
Mikołaj Krupski (University of Warsaw)
On Lindel\"of scattered W-spaces
Aviles and the speaker proved last year that every Lindel\"of scattered subspace of a $ \Sigma$-product of first-countable spaces is $\sigma$-compact. In my talk I will present a generalization of this result to the class …
March 4, 2026, 4:15 p.m.
Piotr Zakrzewski (University of Warsaw)
Some remarks concerning the cardinal min{r,d}
The talk is closely related to the results from a joint article with Roman Pol and Lyubomyr Zdomskyy (see arXiv:2502.20887). In that paper we introduced a cardinal d^* as the smallest κ such that any …
Feb. 25, 2026, 4:15 p.m.
Maciej Malicki (University of Warsaw)
A logic of co-valuations, Part II
A co-valuation is, essentially, a minimal finite cover. We introduce a logic based on co-valuations, which play the role of valuations of free variables in classical first-order logic, and show that the fundamental tools of …
Jan. 21, 2026, 4:15 p.m.
Maciej Malicki (University of Warsaw)
A logic of co-valuations, Part II - canceled
A co-valuation is, essentially, a minimal finite cover. We introduce a logic based on co-valuations, which play the role of valuations of free variables in classical first-order logic, and show that the fundamental tools of …
Jan. 14, 2026, 4:15 p.m.
Jan Rossa (University of Warsaw)
A certain dichotomy for analytic subfamilies of P(N)
In this talk we will discuss a complete proof of a certain dichotomy for analytic subfamilies of P(N) (endowed with the Cantor set topology via characteristic functions), originally stated in G. Godefroy's work "Compacts de …
Jan. 7, 2026, 4:15 p.m.
Maciej Malicki (University of Warsaw)
A logic of co-valuations
A co-valuation is, essentially, a minimal finite cover. We introduce a logic based on co-valuations, which play the role of valuations of free variables in classical first-order logic, and show that the fundamental tools of …
Dec. 17, 2025, 4:15 p.m.
Tomasz Kania (Jagiellonian University)
Polish spaces of categories enriched over separable Banach spaces
We employ the Godefroy--Saint-Raymond machinery of admissible topologies to projectively universal objects in categories such as (separable) Banach spaces, Banach lattices, Banach lattices, C*-algebras etc. as well as countable objects such as groups or rings …
Dec. 10, 2025, 4:15 p.m.
Tomasz Weiss (Cardinal Stefan Wyszynski University in Warsaw)
On the class of (E,M)* sets
We shall say that a subset X of the Cantor space 2^\omega, belongs to the class (E,M)* if, for each F_\sigma measure zero subset F of 2^\omega, the algebraic sum X+F is meager in 2^\omega. …
Dec. 3, 2025, 4:15 p.m.
Piotr Szewczak (Cardinal Stefan Wyszynski University in Warsaw)
Universally meager sets in the Miller model and similar ones
A subset X of the Cantor cube 2^\omega is universally meager, if every Borel isomorphic image of X is meager in 2^\omega. We prove that in the Miller model and in a model constructed by …