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

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 …
May 17, 2017, 4:15 p.m.
Tomasz Cieśla (University of Warsaw)
Borel circle squaring - part 3
In 1925 Alfred Tarski asked whether a square is equidecomposable by isometries with a disc of the same area. This question was answered in the affirmative in 1990 by Laczkovich. In 2015 Grabowski, Mathe and …
May 10, 2017, 4:15 p.m.
Tomasz Cieśla (University of Warsaw)
Borel circle squaring - part 2
In 1925 Alfred Tarski asked whether a square is equidecomposable by isometries with a disc of the same area. This question was answered in the affirmative in 1990 by Laczkovich. In 2015 Grabowski, Mathe and …
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April 26, 2017, 4:15 p.m.
Witold Marciszewski (University of Warsaw)
Extension operators and twisted sums - part 3.
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March 29, 2017, 4:15 p.m.
Martin Dolezal (University of Warsaw)
Sigma-porosity and infinite games
We introduce an infinite game characterizing various types of sigma-porosity for Souslin sets in terms of winning strategies. We use the game to prove and reprove some new and older inscribing theorems for sigma-ideals of …
March 22, 2017, 4:15 p.m.
Grzegorz Plebanek (University of Wrocław )
Boolean algebras and small independent families
We consider Boolean algebras generated by families that can be decomposed into countably many pieces so that no part contains an infinite independent sequence. The property is denoted by WRN because it is closely related …
March 15, 2017, 4:15 p.m.
Tomasz Cieśla (University of Warsaw)
Borel circle squaring
In 1925 Alfred Tarski asked whether a square is equidecomposable by isometries with a disc of the same area. This question was answered in the affirmative in 1990 by Laczkovich. In 2015 Grabowski, Mathe and …
March 8, 2017, 4:15 p.m.
Jacek Tryba (University of Gdańsk)
Homogeneity of ideals
The homogeneity family of the ideal I is a family of subsets such that the restriction of I to this subset is isomorphic to I. We say that an ideal I is homogeneous if all …
March 1, 2017, 4:15 p.m.
Witold Marciszewski (Uniwersytet Warszawski)
Extension operators and twisted sums - part 2.