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

Feb. 28, 2018, 4:15 p.m.
TOMASZ NATKANIEC (University of Gdańsk)
PERFECTLY EVERYWHERE SURJECTIVE BUT NOT JONES FUNCTIONS
Given a function f : R → R we say that • f is perfectly surjective (f ∈ PES) if f[P] = R for every perfect set P; • f is a Jones function (f …
Jan. 24, 2018, 4:15 p.m.
Taras Banakh (Lviv National University and UJK Kielce)
Null-finite sets in metric groups and their applications
We shall introduce a new family of "small" sets which is tightly connected with two well known $\sigma$-ideals: of Haar-null sets and of Haar-meager sets. We define a subset $A$ of a topological group $X$ …
Jan. 17, 2018, 4:15 p.m.
Szymon Żeberski (Wrocław University of Technology)
Nonmeasurable sets and unions with respect to tree ideals
We consider a notion of nonmeasurablity with respect to Marczewski and Marczewski-like tree ideals $s_0$, $m_0$, $l_0$, and $cl_0$. We show that there exists a subset $A$ of the Baire space $\omega^\omega$ which is $s$-, …
Dec. 20, 2017, 4:15 p.m.
Damian Sobota (Kurt Gödel Research Center for Mathematical Logic)
Convergence of measures and cardinal characteristics of the continuum
Let A be a Boolean algebra. We say that A has the Nikodym property if every pointwise convergent sequence of measures on A is weak* convergent. Similarly, A has the Grothendieck property if every weak* …
Dec. 13, 2017, 4:15 p.m.
Tomasz Cieśla (University of Warsaw)
Homeomorphism relation of locally connected continua is complete
Every Borel action of a Polish group G on a Polish space X gives rise to a relation ~ given by x ~ y if and only if x and y are in the same …
Nov. 29, 2017, 4:15 p.m.
Ziemowit Kostana (University of Warsaw)
Non-measurability of the algebraic sums of sets of real numbers
Consider the following problems: 1. If A is a meagre (null) subset of the real line, does there necessarily exist a set B such that the algebraic sum A+B doesn't have the Baire property (is …
Nov. 22, 2017, 4:15 p.m.
Maciej Malicki (Warsaw School of Economics)
Generic representations of countable groups - part 2
The fact that a Polish group G has a comeager conjugacy class can be expressed in the language of representations: it is equivalent to the existence of a generic representation of the group of integers …
Nov. 15, 2017, 4:15 p.m.
Maciej Malicki (Warsaw School of Economics)
Generic representations of countable groups
The fact that a Polish group G has a comeager conjugacy class can be expressed in the language of representations: it is equivalent to the existence of a generic representation of the group of integers …
Nov. 8, 2017, 4:15 p.m.
Yurii Khomskii (Hamburg University)
Definable Maximal Independent Families
Maximal independent families are combinatorial objects that have applications in various areas of mathematics. A maximal independent family can be constructed using the Axiom of Choice, and an old result of Arnold Miller shows that …
Oct. 25, 2017, 4:15 p.m.
Marek Balcerzak (Politechnika Łódzka)
The Baire category of ideal convergent subseries and rearrangements of a divergent series
Let I be a 1-shift-invariant ideal on N with the Baire property. Assume that a series with terms in a real Banach space X is not unconditionally convergent. We show that the sets of I-convergent …
Oct. 18, 2017, 4:15 p.m.
Michał Korch (UW)
Specjalne podzbiory uogólnionej przestrzeni Cantora II / Special subsets of the generalized Cantor space II
Streszczenie: Mój referat zacznie się od wprowadzenia uogólnionej przestrzeni Cantora 2^\kappa dla regularnej nieprzeliczalnej liczby kardynalnej \kappa. Przestrzeń ta wyposażona jest w tak zwaną ograniczoną topologię, generowaną przez zbiory wszystkich przedłużeń funkcji częściowych. W ostatnich …
Oct. 11, 2017, 4:15 p.m.
Michał Korch (UW)
Specjalne podzbiory uogólnionej przestrzeni Cantora / Special subsets of the generalized Cantor space
Streszczenie: Mój referat zacznie się od wprowadzenia uogólnionej przestrzeni Cantora 2^\kappa dla regularnej nieprzeliczalnej liczby kardynalnej \kappa. Przestrzeń ta wyposażona jest w tak zwaną ograniczoną topologię, generowaną przez zbiory wszystkich przedłużeń funkcji częściowych. W ostatnich …
June 7, 2017, 4:15 p.m.
Jarosław Swaczyna (Łódź University of Technology)
Haar-like smallness in Polish groups
In locally compact Polish groups there is a very natural $\sigma$-ideal of null sets with respect to Haar-measure. In non locally compact groups there is no Haar measure, however Christensen introduced a notion of Haar-null …
May 31, 2017, 4:15 p.m.
Piotr Szewczak (Cardinal Stefan Wyszyński University in Warsaw)
The Scheepers property and products of Menger spaces
A topological space X is Menger if for every sequence of open covers O_1, O_2,... of the space X, there are ﬁnite subfamilies F_1\subseteq O_1, F_2\subseteq O_2,... such that their union is a cover of …
May 24, 2017, 4:15 p.m.
Piotr Koszmider (Institute of Mathematics of the Polish Academy of Sciences)
A nonseparable scattered C*-algebra without nonseparable commutative subalgebras
The talk is based on the paper T. Bice, P. Koszmider, A note on the Akemann-Doner and Farah-Wofsey constructions, PAMS 145 (2017), no. 2, 681–687, where we remove the continuum hypothesis from the previous construction …