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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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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 (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 …
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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 …
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Nov. 19, 2025, 4:15 p.m.
Piotr Koszmider (IM PAN)
Boolean algebras and the Calkin algebra
The Calkin C*-algebra Q can be considered as the non-abelian analogue of the Boolean algebra P(N)/Fin. It is defined as the quotient B/K of the algebra B of all linear bounded operators on a separable …
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Nov. 12, 2025, 4:15 p.m.
Kacper Kucharski (Doctoral School of Exact and Natural Sciences UW)
The hereditary Baire property of first-countable perfect spaces is A-invariant
During this talk we will prove that if X and Y are first–countable perfect spaces, such that their free Abelian topological groups A(X) and A(Y) are topologically isomorphic, then X is a hereditary Baire space …
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Nov. 5, 2025, 4:15 p.m.
Damian Sobota (Universität Wien, Kurt Gödel Research Center for Mathematical Logic)
Borel Boolean algebras with the Nikodym property but without the Grothendieck property
I will present a construction of continuum many pairwise non-isomorphic Boolean subalgebras of the power set P(\omega) which have the Nikodym property but not the Grothendieck property and belong to the class F_{\sigma\delta} when thought …
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Oct. 29, 2025, 4:15 p.m.
Grzegorz Plebanek (University of Wrocław)
Banach-Mazur distances between some C(K) spaces
The Banach-Mazur distance between two Banach spaces X and Y can be defined as the infimum of the norms of all norm-increasing isomorphisms T:X --> Y. We present several lower bounds of Banach-Mazur distances between …
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Oct. 22, 2025, 4:15 p.m.
Kacper Kucharski (Doctoral School of Exact and Natural Sciences UW)
Preservation of scattered-like properties by isomorphisms of function spaces and free Abelian topological groups
During the talk we will show that if a space X either satisfies the property (κ) or is strongly σ–scattered, then a space Y has to satisfy the same property, provided there exists a continuous …
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Oct. 15, 2025, 4:15 p.m.
Małgorzata Rojek (Doctoral School of Exact and Natural Sciences UW)
Almost disjoint families and some automorphic and injective properties of $\ell_\infty/c_0$
The question whether any isomorphism between two isomorphic copies of $c_0(\omega_1)$ in $\ell_\infty/c_0$ can be extended to an automorphism of the whole space was posed by A. Aviles, F. Cabello Sanchez, J. Castillo, M. Gonzalez …
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Aug. 13, 2025, 10 a.m.
Andre Nies (University of Auckland)
Complexity of the isomorphism relation for Borel classes of non Archimedean groups
In the paper "The complexity of topological group isomorphism", JSL 2018, A. Kechris, the speaker and K. Tent, started the programme to determine the Borel complexity of the isomorphism relation for natural Borel classes of …
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June 11, 2025, 4:15 p.m.
Ziemowit Kostana (Wrocław University of Science and Technology)
Diamond on Kurepa trees
We investigate a weak variant of Jensen's Diamond, which is expected to guess only cofinal branches of a specific Kurepa tree. We prove that in many scenarios such principle holds. Nevertheless, it is consistent that …
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June 4, 2025, 4:15 p.m.
Luis David Reyes Saenz (National Autonomous University of Mexico)
Isomorphic C(K) spaces from Almost Disjoint families
The construction of the Alexandrov-Urysohn (AU) compacta out of Almost Disjoint (AD) families, as well as the space of continuos functions over these compacta, have been intensively studied in recent years. In the present talk …
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May 28, 2025, 4:15 p.m.
Piotr Zakrzewski (University of Warsaw)
On uniform continuity of monotone functions
The main subject of this talk is the statement that for every non-decreasing function f : [0, 1] −→ [0, 1], each subset of [0, 1] of cardinality c contains a set of cardinality c …
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May 21, 2025, 4:15 p.m.
Piotr Szewczak (Cardinal Stefan Wyszynski University in Warsaw)
Hurewicz's property and concentrated sets in the Laver model
Let X be a set of reals. The set X is Hurewicz if for any sequence of countable increasing open covers of X one can select a single element from each cover such that the …
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May 14, 2025, 4:15 p.m.
Sven Manthe (University of Bonn)
The Borel monadic theory of order is decidable
The monadic second-order theory S1S of (ℕ,<) is decidable (it essentially describes ω-automata). Undecidability of the monadic theory of (ℝ,<) was proven by Shelah. Previously, Rabin proved decidability if the monadic quantifier is restricted to …
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May 7, 2025, 4:15 p.m.
Rafał Filipów (Rafał Filipów)
Critical ideals for compact spaces and Borel complexity of sets of ideal limit points
In the first part of my talk, I will introduce an ideal conv_alpha and use it to characterize (with the aid of the Katetov order) the class of all compact countable spaces which are homeomorphic …
