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 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 …
Nov. 26, 2025, 4:15 p.m.
Julia Ścisłowska (Doctoral School of Exact and Natural Sciences UW)
Two new stories from the land of ultrafilter orders
The main goal of the talk is to discuss two topics concerning ultrafilter orders on chainable continua: order type of ultrafilter orders on chainable continua and descriptive complexity of ultrafilter orders on chainable continua. During …