Weekly research seminar
Organizers
 prof. dr hab. Mikołaj Bojańczyk
 prof. dr hab. Damian Niwiński
Information
Wednesdays, 2:15 p.m. , room: 5050Research fields
List of talks

July 5, 2023, 2:15 p.m.
Michał Gajda (MigaMake Pte Ltd, Singapur)
Semigroup decomposition and semigroup transformers
KrohnRhodes theorem claims that every semigroup can be decomposed into finite groups, and aperiodic semigroups. This theorem has been generalized from finite semigroups to infinite ones, but uses a hairy construct of a wreath product, …

June 21, 2023, 2:15 p.m.
Damian Niwiński (MIM UW)
On the complexity of conditional independence
A conditional independence statement says that, for example, random variables (X,Y) and (W,Y,Z) are independent given a random variable (U,V). Cheuk Ting Li showed in 2022 that it is undecidable if a Boolean combination of …

June 14, 2023, 2:15 p.m.
Nathanaël Fijalkow (CNRS, LaBRI, University of Bordeaux & MIM UW)
Sampling and enumerating for probabilistic contextfree grammars
I'll discuss algorithms for sampling and enumerating terms from a given probabilistic contextfree grammar. It will be mostly a "Not my theorem" session, with early contributions from back in 1974, but if time permits I'll …

June 7, 2023, 2:15 p.m.
Pierre Ohlmann (MIM UW)
Finite versus infinite arenas for positionality in infinite duration games
This talk is about positionality (for the protagonist) in infinite duration games, either over finite or over arbitrary arenas. The aim is to compare the two notions. Classically, it is well known that the parity …

May 31, 2023, 2:15 p.m.
Szymon Toruńczyk (MIM UW)
Flipwidth
I will define a new graph parameter called flipwidth. Graph classes of bounded flipwidth include classes of bounded expansion of Nesetril and Ossona de Mendez, as well as classes of bounded twinwidth of Bonnet, Kim, …

May 24, 2023, 2:15 p.m.
Mikołaj Bojańczyk (MIM UW)
A categorical characterisation of linear regular functions
We consider linear regular stringtostring functions, i.e. functions that are recognized by copyless streaming string transducers, or any of their equivalent models, such as deterministic twoway automata. Although this class of functions is clearly important, …

May 17, 2023, 2:15 p.m.
Liat Peterfreund (CNRS, LIGM, ParisEst University)
Querying incomplete numerical data: between certain and possible answers
Queries with aggregation and arithmetic operations, as well as incomplete data, are common in realworld databases, but we lack a good understanding of how they should interact. On the one hand, systems based on SQL …

May 10, 2023, 2:15 p.m.
Nikolas Mählmann (University of Bremen)
Monadically Stable Classes of Graphs
Intuitively, a class of graphs is monadically stable if firstorder logic cannot encode arbitrary long linear orders in it. While originating from model theory, monadic stability generalizes many combinatorial properties of sparse graph classes such …

April 26, 2023, 2:15 p.m.
Yoàv Montacute (University of Cambridge)
Logic and Dynamical Systems
The study of the relationship between logic and topology has a rich and extensive history. One way of exploring this relationship involves examining the formal languages of indiscrete spaces and their discrete representations. The talk …

April 19, 2023, 2:15 p.m.
Lorenzo Clemente (MIM UW)
Equality and zeroness problems of power series for combinatorial enumeration
A power series is constructible differentially finite (CDF) if it satisfies a system of polynomial differential equations [Bergeron & Reutenauer 1990, Bergeron & Sattler 1995]. CDF series generalise algebraic power series and find a natural …

April 12, 2023, 2:15 p.m.
Mikołaj Bojańczyk (MIM UW)
On the growth rate of polyregular functions
Polyregular functions are stringtostring functions that have polynomial size outputs. I will show that a polyregular function has growth rate O(n^k) if and only if it can be defined by an mso transduction of dimension …

April 5, 2023, 2:15 p.m.
Roland Guttenberg (TU Munich)
Geometry of Vector Addition Systems
We will prove the missing line conjecture for VAS. The proof proceeds in three steps, all based on the basic units of VAS: Periodic sets. 1) Prove an easy special case. 2) Explain all closure …

March 29, 2023, 2:15 p.m.
Giannos Stamoulis (LIRMM, Université de Montpellier, CNRS)
Model Checking DisjointPaths Logic on TopologicalMinorFree Graph Classes
Disjointpaths logic, denoted FO+DP, extends firstorder logic (FO) with atomic predicates dp_k[(x_1, y_1),…,(x_k, y_k)], expressing the existence of internally vertexdisjoint paths between x_i and y_i, for 1 ≤ i ≤ k. In this talk, we …

March 22, 2023, 2:15 p.m.
Wojciech Przybyszewski (MIM UW)
Reproving combinatorial properties of nowheredense graphs using model theory
A pinnacle of sparsity theory, initiated by Ossona de Mendez and Nešetřil, is the result of Grohe, Kreutzer, and Siebertz which identifies subgrafclosed classes of graphs with FPT model checking as exactly nowhere dense classes. …

March 15, 2023, 2:15 p.m.
Arka Ghosh (MIM UW)
Orbitfinite systems of inequalities
A system of inequalities is orbitfinite if it is finite up to certain permutations of variables. In this talk, I will describe this concept using interesting examples, and present our recent results on the solvability …