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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: 5050Research fields
List of talks
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March 23, 2022, 4:15 p.m.
Piotr Szewczak (Cardinal Stefan Wyszyński University in Warsaw)
Strongly sequentially separable function spaces
A space is Frechet–Urysohn if each point in the closure of a set is a limit of a sequence from the set. A separable space is strongly sequentially separable if, for each countable dense set, …
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March 16, 2022, 4:15 p.m.
Piotr Koszmider (IM PAN)
Almost disjoint families and the geometry of spheres
We present an example of a nonseparable Banach space where every uncountable subset of the unit sphere contains two vectors which are distant by less than one. This solves in the negative the central problem …
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Jan. 26, 2022, 4:15 p.m.
Taras Banakh (Ivan Franko National University of Lviv and UJK Kielce)
Automatic continuity of measurable homomorphisms on topological groups
We shall discuss three recent results on automatic continuity of homomorphisms: 1) Every Haar-measurable homomorphism from a locally compact group to an arbitrary topological group is continuous. 2) Every homomorphism with the Baire property from …
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Jan. 19, 2022, 4:15 p.m.
Wiesław Kubiś (Cardinal Stefan Wyszyński University in Warsaw and Institute of Mathematics of the Czech Academy of Sciences)
Abstract evolution systems, amalgamation and homogeneity
An evolution system is just a category with a distinguished class of arrows, called transitions. This concept, in particular, generalizes abstract rewriting system. It turns out that evolution systems with amalgamation provide a good framework …
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Jan. 12, 2022, 4:15 p.m.
Maciej Malicki (IMPAN)
Large conjugacy classes and weak amalgamation
Ivanov, and later Kechris and Rosendal, characterized the existence of dense or comeager (diagonal) conjugacy classes in automorphism groups of certain classes of Fraïssé limits. I will show how these results can be extended to …
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Dec. 15, 2021, 4:15 p.m.
Sławomir Solecki (Cornell University)
Closed groups generated by generic measure preserving transformations
The behavior of a measure preserving transformation, even a generic one, is highly nonuniform. In contrast to this observation, a different picture of a very uniform behavior of the closed group generated by a generic …
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Dec. 8, 2021, 4:15 p.m.
Paul Szeptycki (York University)
On a topological Ramsey theorem
This is joint work with Wiesław Kubiś. We introduce natural strengthenings of sequential compactness called the $r$-Ramsey property for each natural number $r\geq 1$. We prove that metrizable compact spaces are $r$-Ramsey for all $r$ …
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Dec. 1, 2021, 4:15 p.m.
Piotr Szewczak (Cardinal Stefan Wyszyński University in Warsaw)
Products of Hurewicz, Menger and Lindelof spaces - a continuation
We consider products of general topological spaces with Hurewicz’s, Menger’s and Lindelof’s covering properties. Assuming the Continuum Hypothesis, we prove that every productively Lindelof space is productively Menger, and every productively Menger space is productively …
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Nov. 24, 2021, 4:15 p.m.
Alberto Salguero Alarcón (Universidad de Extremadura, Badajoz, Spain)
K)-space is not a three-space propert (To be a C)
In the setting of Banach spaces, a property P is said to be a three-space property if whenever a Banach space X has a subspace Y so that both Y and the quotient space X/Y …
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Nov. 17, 2021, 4:15 p.m.
Jan van Mill (University of Amsterdam)
Universal autohomeomorphisms of $N^*$
This is joint work with Klaas Pieter Hart. We study the existence of universal autohomeomorphisms of $N^*$. We prove that CH implies there is such an autohomeomorphism and show that there are none in any …
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Nov. 3, 2021, 4:15 p.m.
Piotr Szewczak (Cardinal Stefan Wyszyński University in Warsaw)
Products of Hurewicz, Menger and Lindelof spaces
We consider products of general topological spaces with Hurewicz’s, Menger’s and Lindelof’s covering properties. Assuming the Continuum Hypothesis, we prove that every productively Lindelof space is productively Menger, and every productively Menger space is productively …
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Oct. 27, 2021, 4:15 p.m.
Grzegorz Plebanek (University of Wrocław)
On kappa-Corson compacta
A compact space is `Corson compact' if it can be embedded into some product of real lines in such a way that the support of every element is countable; kappa-Corson compactness is defined in the …
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Oct. 20, 2021, 4:15 p.m.
Jacek Tryba (University of Gdańsk)
Different kinds of density ideals
We consider several kinds of ideals described by some densities. We present connections between Erdos-Ulam, density, matrix summability and generalized density ideals and show that a certain inaccuracy in Farah's definition of density ideals leads …
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Oct. 13, 2021, 4:15 p.m.
Tomasz Weiss (Cardinal Wyszyński University in Warsaw)
On the algebraic sum of a perfect set and a large subset of the reals
In M. Kysiak’s paper "Nonmeasurable algebraic sums of sets of reals", (Coll. Math., Vol. 102, No 1, 2005), the following two questions appeared. Assume that A ⊆ R is a non-meager set with the Baire …
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June 9, 2021, 4:15 p.m.
Krzysztof Zakrzewski (University of Warsaw)
Rosenthal compacta and lexicographic products
For a metrizable space X, by B_1(X) we denote the space of real valued functions of the first Baire class on X, endowed with pointwise convergence topology. A compact space K is called Rosenthal compact …
