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

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 …
Dec. 12, 2018, 4:15 p.m.
Andrzej Starosolski (Silesian University of Technology)
a continuation (The Rudin–Keisler ordering of P-points under b = c)
M. E. Rudin (1971) proved, under CH, that for each P-point there exists a P-point strictly RK-greater. This result was proved under p = c by A. Blass (1973), who also showed that each RK-increasing …
Dec. 5, 2018, 4:15 p.m.
Andrzej Starosolski (Silesian University of Technology)
The Rudin–Keisler ordering of P-points under b = c
M. E. Rudin (1971) proved, under CH, that for each P-point there exists a P-point strictly RK-greater. This result was proved under p = c by A. Blass (1973), who also showed that each RK-increasing …
Nov. 28, 2018, 4:15 p.m.
Wiesław Kubiś (Cardinal Stefan Wyszyński University in Warsaw and Institute of Mathematics of the Czech Academy of Sciences)
Uniform homogeneity
A mathematical structure is called homogeneous if every isomorphism between its ``small" substructures extends to an automorphism. If additionally, this extension can be made algebraic, namely, preserving compositions, we then say that the structure is …
Nov. 21, 2018, 4:15 p.m.
Grzegorz Plebanek (University of Wrocław)
On Cartesian products of compact lines
This is joint work with Gonzalo Martinez Cervantes. By a compact line we mean a compact space which topology is defined by a linear order. Answering a problem posed by Mardesic, we show that n-fold …
Nov. 14, 2018, 4:15 p.m.
Arturo Antonio Martínez Celis Rodríguez (IMPAN)
Ultrafilters related to the Michael space problem
A Lindelöf Topological space is Michael if it has non-Lindelöf product with the space of the irrational numbers. These kind of spaces were introduced by Ernest Michael in 1963 and it is still unknown if …
Nov. 7, 2018, 4:15 p.m.
Ali Enayat (University of Gothenburg, Sweden)
Models of arithmetic meet set theory and topology
The first part of the talk is expository and provides a general introduction to nonstandard models of arithmetic, and the various ways they interact with set theory and topology. The second part focuses on recent …
Oct. 24, 2018, 4:15 p.m.
Paweł Krupski (Wrocław University of Science and Technology)
Complexity of homeomorphism relations on some classes of compacta
This is a joint work with Benjamin Vejnar (https://arxiv.org/pdf/1808.08760.pdf). We prove that the homeomorphism relation between compact spaces can be continuously reduced to the homeomorphism equivalence relation between absolute retracts which strengthens and simplifies recent …
Oct. 17, 2018, 4:15 p.m.
Roman Pol (University of Warsaw)
On a problem of Talagrand concerning separately continuous functions
This is a joint work with Volodymyr Mykhaylyuk (a preliminary version of our paper is on arXiv: https://arxiv.org/pdf/1809.05799.pdf) M.Talagrand [Math.Ann.270(1985),Probleme 3] stated the following problem (recalled recently in Guirao, V.Montesinos, V.Zizler, Open problems in …