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Weekly research seminar
Organizers
- prof. dr hab. Witold Marciszewski
- prof. dr hab. Piotr Zakrzewski
Information
Wednesdays, 4:15 p.m. , room: 4050Research fields
List of talks
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Oct. 28, 2026, 4:15 p.m.
Ronnie Chen (University of Warsaw)
On locally countable Borel trees, graphs, equivalence relations, and other structures
This talk concerns locally countable Borel combinatorial structures, such as graphs, trees, group actions, etc., on Polish spaces (or standard Borel spaces). There is a rich framework, developed over the past four decades by many …
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Oct. 14, 2026, 4:15 p.m.
Kamil Ryduchowski (University of Warsaw)
A Banach space C(K) picky about its biorthogonal systems.
For a non-metrizable zero-dimensional compact Hausdorff space K a biorthogonal system in C(K) is a sequence (f_alpha, mu_alpha) of pairs such that f_alpha is a continuous function on K, mu_alpha is a Radon measure on …
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June 10, 2026, 4:15 p.m.
Tanmay Inamdar
A Ramsey theorem for the reals
The infinite Ramsey theorem states that for any colouring of pairs of natural numbers (or triples, quadruples etc.) into finitely-many colours, there is an infinite set which is monochromatic. Sierpinski proved that there is no …
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June 3, 2026, 4:15 p.m.
Maksymilian Wesoły (University of Warsaw)
Between the classes of semi-Eberlein and Valdivia compact spaces
Recently Todorcevic has introduced the hierarchy of E_2(\theta) compact spaces. Motivated by the definition of Valdivia compact spaces, we introduce a corresponding hierarchy of semi-E_2(\theta) compacta. We investigate how these classes behave under Alexandroff duplicates. …
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May 27, 2026, 4:15 p.m.
Tomasz Żuchowski (University of Wrocław)
On cardinal invariants related to Rosenthal families and large-scale topology
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May 20, 2026, 4:15 p.m.
Julia Filip (University of Warsaw)
Order structure of the class of compactifications of omega
The class of compactifications of a given topological space X can be endowed with a natural partial (pre)order. We will discuss the properties of such an order for the simplest non-trivial topological space - omega, …
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May 13, 2026, 4:15 p.m.
Antonio Acuaviva (Lancaster University)
C(K)-spaces with few operators relative to posets
Understanding the closed operator ideals of the algebra of operators on a Banach space is a natural but often difficult problem. In this talk, we will focus on the case of spaces of continuous functions, …
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May 6, 2026, 4:15 p.m.
Witold Marciszewski (University of Warsaw)
Roman Pol's example of a Hurewicz set with one-dimensional square
Paul Erdos gave an example of a closed one-dimensional subspace X of a Hilbert space whose square X x X is also one-dimensional. On the other hand, it is known that such example cannot be …
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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 …
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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 …
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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 $C_p(K)$ …
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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 …
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March 25, 2026, 4:15 p.m.
Ruiyuan Chen (University of Warsaw)
Orbitwise topologies and quasi-Polish techniques for Polish group actions
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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 …
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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 …
