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

May 29, 2024, 2:15 p.m.
Filip Mazowiecki (University of Warsaw)
Determinisation and Unambiguisation of PolynomiallyAmbiguous Rational Weighted Automata
We study the determinisation and unambiguisation problems of weighted automata over the rational field: given a weighted automaton, can we determine whether there exists an equivalent deterministic, respectively unambiguous, weighted automaton? Recent results by Bell …

May 22, 2024, 2:15 p.m.
Jakub Kozik (Jagiellonian University)
Choosability version of Thue's theorem on nonrepetitive sequences
Pattern avoidance is a deeply studied problem within the field of combinatorics on words. One of the seminal results of this area is the theorem of Thue which asserts that there exists an infinite word …

May 15, 2024, 2:15 p.m.
Igor Walukiewicz (CNRS, LaBRI, Bordeaux University)
Rethinking PartialOrder Methods
The goal of partialorder methods is to speed up explicit state exploration of concurrent systems. The state space of these systems grows exponentially with the number of components. Yet, explicit state exploration remains one of …

April 24, 2024, 2:15 p.m.
Gorav Jindal (Max Planck Institute for Software Systems)
Sign Me Up: PosSLP, Sign Testing, and Polynomials
Given an integer, deciding its positivity may appear trivial initially. However, this problem becomes more compelling when the integer is presented in a compact form, as opposed to being explicitly represented as a bit string. …

April 17, 2024, 2:15 p.m.
Shuo Pang (University of Copenhagen)
Supercritical and Robust Tradeoffs for Resolution Depth Versus Width and Weisfeiler–Leman
We give the first robust resolution tradeoffs for which low width implies depth superlinear in the formula size. We show analogous results for the Weisfeiler–Leman algorithm, which also translate into tradeoffs between number of variables …

April 10, 2024, 2:15 p.m.
Clotilde Biziere (University of Warsaw / ENS Paris)
Reachability in 2dimensional Branching Vector Addition Systems with States
Vector addition systems with states (VASS) are finitestate machines equipped with a finite number of counters ranging over nonnegative integers. Operations on counters are limited to incrementation and decrementation. Their central algorithmic problem is reachability: …


March 27, 2024, 2:15 p.m.
Tim Seppelt (RWTH Aachen University)
Homomorphism Indistinguishability: Characterisations, Closure, Complexity
In 1967, Lovász proved that two graphs G and H are isomorphic iff they are homomorphism indistinguishable over the the family of all graphs, i.e. for all graphs F the number of homomorphisms from F …

March 20, 2024, 2:15 p.m.
Jingjie Yang (University of Oxford)
Equivariant subspaces of orbitfinitedimensional vector spaces
In their LICS21 paper, Bojańczyk, Klin, and Moerman gave an equivalence algorithm for weighted orbitfinite automata: they construct a chain of configuration spaces that are closed under both linear combinations and atom permutations; crucially, termination …

March 13, 2024, 2:15 p.m.
Alexandra Rogova
Connecting graph and relational query languages
Practical query languages for graph and relational databases are based on similar concepts: In the former, base relations are extracted from graphs, and in the latter, they are given as input. In both, these base …

March 6, 2024, 2:15 p.m.
Szymon Toruńczyk (MIMUW)
Combinatorial Characterizations of Monadically Dependent Graph Classes
We provide the first two combinatorial characterizations of monadically dependent graph classes. This yields the following dichotomy. On the structure side, we characterize monadic dependence by a property called flipbreakability. This notion generalizes the notions …

Feb. 28, 2024, 2:15 p.m.
Michał Pilipczuk (MIMUW)
FirstOrder Model Checking on Monadically Stable Graph Classes
A graph class C is monadically stable if one cannot interpret arbitrary long linear orders in colored graphs from C using any fixed firstorder interpretation. We prove that on any monadically stable class, the modelchecking …

Feb. 21, 2024, 2:15 p.m.
Vincent Michielini (University of Warsaw)
Complexity of Maslov's Class Kbar
Maslov’s class Kbar is a fragment of FirstOrder Logic consisting of formulae in NNF whose variables occurring in the different atoms obey a certain pattern [*]. It embeds many wellknown fragments, such as the twovariable …

Feb. 14, 2024, 2:15 p.m.
Daniel Smertnig (University of Ljubljana)
On the linear hull of a weighted automaton
Previous work reduces the problem of deciding whether a weighted finite automaton (WFA) over a field is equivalent to a deterministic, respectively, unambiguous, WFA to the computation of the linear hull. The linear hull is …

Feb. 7, 2024, 2:15 p.m.
Mikołaj Bojańczyk (University of Warsaw)
On function spaces for orbitfinite sets
Joint work with Tito Nguyen and Rafał Stefański. Orbitfinite sets are a generalisation of finite sets, and as such support many operations allowed for finite sets, such as pairing, quotienting, or taking subsets. However, they …