Organizers

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

Information

Wednesdays, 4:15 p.m. , room: 5050

Research fields

Topology and Set Theory

List of talks

June 12, 2019, 4:15 p.m.
Mikołaj Krupski (University of Warsaw)
Embedding of the Free Abelian Topological Group A(X x X) into A(X)
In my talk I will discuss the following question: For which separable metrizable spaces X does the free abelian topological group A(X x X) isomorphically embed into A(X)? While for many natural spaces X such …
June 5, 2019, 4:15 p.m.
Piotr Koszmider (IMPAN)
On R-embeddability of almost disjoint families and some problems concerning C*-algebras
An almost disjoint family A of subsets of N is said to be R-embeddable if there is a function f:N→R such that the sets f[A] are ranges of real sequences converging to distinct reals for …
May 29, 2019, 4:15 p.m.
Tomasz Weiss (Cardinal Wyszyński University in Warsaw)
Some properties of the * operation on families of special subsets of R. Algebraic sum of a perfect set and large subsets of R
In the first part of this talk I will present the following lemma. Assume CH. Given a non trivial ideal F of subsets of R which is Borel supported, translation invariant, with cov(F) =c/the continuum/ …
May 22, 2019, 4:15 p.m.
Tomasz Cieśla (McGill University)
Measurable Hall's theorem for actions of abelian groups
We prove a measurable version of the Hall marriage theorem for actions of finitely generated abelian groups. In particular, it implies that for free measure-preserving actions of such groups, if two equidistributed measurable sets are …
May 15, 2019, 4:15 p.m.
Witold Marciszewski (University of Warsaw)
Twist and Shout - a continuation
We consider the class of Banach spaces Y for which the space c_0 admits a nontrivial twisted sum with Y, i.e., there exists a Banach space X containing a noncomplemented copy Z of c_0 such …
May 8, 2019, 4:15 p.m.
Witold Marciszewski (University of Warsaw)
Twist and Shout
We consider the class of Banach spaces Y for which the space c_0 admits a nontrivial twisted sum with Y, i.e., there exists a Banach space X containing a noncomplemented copy Z of c_0 such …
April 17, 2019, 4:15 p.m.
Damian Sobota (Kurt Gödel Research Center, University of Vienna)
Selected topics in convergence of measures on compact spaces
During my talk I'll present some most recent results of my joint work with Lyubomyr Zdomskyy concerning different aspects of convergence of sequences of Radon measures on compact spaces. Among others, I'll present a (sketch …
April 10, 2019, 4:15 p.m.
Rafał Górak (Warsaw University of Technology)
A classification of spaces of continuous functions on ordinals
During my talk, I will present the missing case of the topological classification of spaces of continuous real-valued functions Cp([0, \aplha]) on ordinals. This result was recently presented by Genze, Gulko and Khymyleva (https://arxiv.org/pdf/1806.09015.pdf) and …
March 27, 2019, 4:15 p.m.
Jerzy Kąkol (A. Mickiewicz University)
Grothendieck spaces C(K), Efimov spaces, and the separable quotient problem for spaces C_p(X)
The abstract of the talk can be found here: http://www.mimuw.edu.pl/~wmarcisz/Seminarium/Warszawa-27-03.2019.pdf The next meeting of the seminar is planned on April 10th (there will be no meeting on April 3rd).
March 20, 2019, 4:15 p.m.
Ziemowit Kostana (University of Wrocław)
On countably saturated linear orders
We will say that a linear order L is countably saturated if for any two countable subsets A,B of L, such that any element of A is less than any element of B, we can …
March 13, 2019, 4:15 p.m.
Taras Banakh (Ivan Franko National University of Lviv and UJK Kielce)
Universally meager sets and the Baire category property of some function spaces
We shall discuss the problem of inner characterization of topological spaces $X$ for which the space $B_1(X)$ of real-valued Baire class one functions is Baire or Choquet. We prove that for any separable metrizable space …
March 6, 2019, 4:15 p.m.
Piotr Szewczak (Cardinal Wyszyński University in Warsaw)
Products of gamma-sets
Let X be a set of reals and Cp(X) be the set of all continuous real-valued functions on X with the pointwise convergence topology. By the result of Gerlits and Nagy the space Cp(X) has …
Feb. 27, 2019, 4:15 p.m.
Maciej Malicki (Warsaw School of Economics)
Complexity of the isomorphism relation for metric structures
For a given sentence s in the infinitary logic, one can consider the Borel space M of all countable models satisfying s, and the isomorphism equivalence relation E on M. Hjorth and Kechris found a …
Jan. 9, 2019, 4:15 p.m.
Mikołaj Krupski (University of Warsaw)
The functional tightness of infinite products
The functional tightness $t_0(X)$ of a space $X$ is a cardinal invariant related to both the tightness $t(X)$ and the density character $d(X)$ of $X$. While the tightness $t(X)$ measures the minimal cardinality of sets …
Dec. 19, 2018, 4:15 p.m.
Mikołaj Krupski (University of Warsaw)
Games, hereditarily Baire hyperspaces and Mengerness at infinity
A topological space X is Baire if the intersection of a countable family of open dense sets in X is dense. We say that X is hereditarily Baire if every closed subspace of X is …