Planowane seminaria

I will introduce the notion of a coarse dynamical system on an unbounded metric space. A coarse analogue of topological entropy can be defined for these systems that measures the divergence of orbits on the large scale and is invariant under coarse conjugacy. I will discuss some cases where the coarse entropy differs from Bowen’s noncompact topological entropy and some cases where they coincide, as well as work in progress on other coarse dynamical invariants. This is joint work with Michał Misiurewicz.

Title: Spaces of matrices of bounded rank

Joseph Landsberg (Texas A&M University)
Date: 07.10.2026
Time: 14:15
Localisation: r. 321

I'll discuss a classical problem in linear algebra: what are the linear subspaces of a space of mxm matrices where no matrix in the subspace has full rank? This problem has been studied at least since 1949, but little is known about it. I'll describe recent progress on the problem and why we were motivated to study it. This is joint work with Hang (Amy) Huang.

Title: ON MASAS OF THE CALKIN ALGEBRA

Piotr Koszmider (IMPAN, Warszawa, Poland)
Date: 07.10.2026
Time: 17:15
Localisation: r. 321

Masas of the Calkin algebra have proved considerably more elusive than masas of the algebra of bounded operators on a separable Hilbert space. Classical liftable masas fall into only three isomorphism types, while nonliftable examples suggest a much richer picture. I will survey classical results on masas of the Calkin algebra and discuss my recent results. Assuming the Continuum Hypothesis, projection-generated masas admit a complete isomorphic classification: C(K) is *-isomorphic to such a masa precisely when K is compact Hausdorff, totally disconnected, has weight at most the continuum and has no G-delta points. We thus arrive at masas which are group C*-algebras, nonseparable von Neumann algebras, masas admitting conditional expectations and others admitting none, as well as many other exotic examples. Even in ZFC, we can obtain a large family of pairwise nonisomorphic projection-generated masas. I will also discuss recent results showing that the possible densities of masas may depend on additional set-theoretic assumptions, and how the Continuum Hypothesis characterisation may consistently fail. The talk is based on two preprints: arXiv:2512.06580 and arXiv:2609.12916.

Title: Seven tornadoes in one spot: AI and mathematics, summer 2026

Piotr Śniady (IMPAN, Warszawa, Poland)
Date: 08.10.2026
Time: 14:15
Localisation: r. 321

This summer mathematics changed faster than most of us could follow. This is a short status report: facts, not opinions.
Sometimes the role of AI is documented: a self-taught neurosurgery resident obtained a proof of Crouzeix's conjecture from a commercially available AI model. More often we can only reason statistically, as with tornadoes and global warming. I will show a burst of follow-ups on the Komlós conjecture, a group posting claimed solutions in unrelated fields every week, formal proofs in Lean, and a sharp change in arXiv combinatorics

Title: Linear Constraint System Games and the Non-Hyperlinear Group Problem

Prem Nigam Kar (IM PAN, Warszawa, Poland)
Date: 09.10.2026
Time: 10:45
Localisation: r. 106

Linear Constraint System (LCS) games arose in quantum information theory as a generalization of the Mermin-Peres magic square game, which can be used to give an alternative proof of the celebrated Bell’s theorem in quantum mechanics. One can associate a solution group to each LCS game, which encodes its “quantum strategies.” Solution groups and LCS games have played a key role in a number of important results in quantum information theory over the past decade, most notably in the negative resolution of the strong and middle Tsirelson problems by William Slofstra. However, the weak Tsirelson problem, which was solved for general nonlocal games, still remains open for LCS games. In this talk, after a quick introduction to quantum information theory, LCS games, and solution groups, we shall see how the weak Tsirelson problem for LCS games relates to the non-hyperlinear group problem and how the non-hyperlinear group problem itself relates to the non-sofic group problem, which was recently “resolved” by AI.  The only prerequisite for this talk will be a basic understanding of bounded operators on Hilbert spaces.

Title: A subjective overview of the most recent results, part I

Łukasz Stettner (IM PAN, Warszawa, Poland)
Date: 09.10.2026
Time: 12:15
Localisation: r. 6

Title: MULTIPULLBACK C*-ALGEBRAS AND QUANTUM EVEN-DIMENSIONAL SPHERES

Athul P. Gothe (Uniwersytet Warszawski / IMPAN, Warszawa, Poland) 
Date: 09.10.2026
Time: 14:00
Localisation: r. 405

Multipullbacks of C*-algebras were first defined by Pedersen in his seminal paper on pushouts and pullback constructions for C*-algebras (referred to as multirestricted direct sums). These were used to construct the odd-dimensional multipullback quantum spheres and complex projective spaces by Hajac, et al. These C*-algebras are the boundaries of a version of even-dimensional quantum balls given by n-copies of the Toeplitz algebra. Building on this, we define the C*-algebra of multipullback quantum even-dimensional spheres and show that they admit a mutipullback structure akin to the classical construction of a suspension by gluing cones over the base space.

Title: MULTIPULLBACK C*-ALGEBRAS AND QUANTUM EVEN-DIMENSIONAL SPHERES

Athul P. Gothe (Uniwersytet Warszawski / IMPAN, Warszawa, Poland) 
Date: 09.10.2026
Time: 14:00
Localisation: r. 405

Multipullbacks of C*-algebras were first defined by Pedersen in his seminal paper on pushouts and pullback constructions for C*-algebras (referred to as multirestricted direct sums). These were used to construct the odd-dimensional multipullback quantum spheres and complex projective spaces by Hajac, et al. These C*-algebras are the boundaries of a version of even-dimensional quantum balls given by n-copies of the Toeplitz algebra. Building on this, we define the C*-algebra of multipullback quantum even-dimensional spheres and show that they admit a mutipullback structure akin to the classical construction of a suspension by gluing cones over the base space.