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

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 …

Jan. 31, 2024, 2:15 p.m.
Cristian Riveros Jaeger (Pontificia Universidad Católica de Chile (PUC Chile))
#NFA admits an FPRAS
#NFA is the following problem over nondeterministic finite automata (NFA) over words: you receive as input an NFA A and a length N (in unary), and you want to count the number of words of …

Dec. 20, 2023, 2:15 p.m.
Julie Parreaux (University of Warsaw)
Playing stochastically in Weighted Timed Games to Emulate Memory
Weighted timed games are twoplayer zerosum games played in a timed automaton equipped with integer weights. We consider optimal reachability objectives, in which one of the players, that we call Min, wants to reach a …

Dec. 13, 2023, 2:15 p.m.
Lorenzo Clemente (University of Warsaw)
Zeroness of weighted basic parallel processes and other finitely generated classes of series
We consider a weighted model of computation generalising weighted finite automata over fields, namely weighted basic parallel processes (WBPP). The underlying unweighted BPP model, popular in process algebra, was introduced by Christensen in his PhD …

Dec. 6, 2023, 2:15 p.m.
Antonio Casares (University of Warsaw)
A characterization of halfpositionality for omegaregular languages
In the context of infinite duration games over graphs, a central question is: For which objectives can the existential player always play optimally using positional (memoryless) strategies? In this talk, we characterize omegaregular objectives with …

Nov. 29, 2023, 2:15 p.m.
Ruiwen Dong (Saarland University)
Decidability problems in infinite semigroups
This talk is about several algorithmic problems for matrix semigroups. A classic problem in this area is the wellknown Semigroup Membership problem: given as input a finite set of square matrices S = {A1, A2, …

Nov. 22, 2023, 2:15 p.m.
Rafał Stefański (University of Warsaw)
Recognisable transducers over monads and comonads
In 2015, Bojańczyk introduced a class of recognizable languages over monads, which is a common generalization of regular languages for many different types of objects, including words, infinite words, and trees. In this talk, I …

Nov. 8, 2023, 2:15 p.m.
Michał Przybyłek (PolishJapanese Academy of Information Technology)
Some remarks on StoneČech compactification in ZFA
Working in ZermeloFraenkel Set Theory with Atoms over an \omegacategorical \omegastable structure, we show how some infinite constructions over definable sets can be encoded as finite constructions over StoneČech compactification of the sets. In particular, …

Oct. 25, 2023, 2:15 p.m.
Arka Ghosh (University of Warsaw)
Equivariant polynomial ideals
In this joint work with Sławek Lasota we study ideals of polynomials, where variables are elements of a countable logical structure. In this setting we allow structurepreserving embeddings to act on polynomials by renaming variables, …

Oct. 18, 2023, 2:15 p.m.
Aliaume Lopez (University of Warsaw)
From Local to Global Relativization of the Łoś–Tarski Theorem
We consider first order sentences over a finite relational signature σ. Classical preservation theorems, dating back to the 1950s, state the correspondence between syntactic fragments of FO[σ], and semantic ones. The archetypal example of such …

Oct. 11, 2023, 2:15 p.m.
Mikołaj Bojańczyk (University of Warsaw)
Polyregular functions on unordered trees of bounded height
Joint work with Bartek Klin (University of Oxford) We consider firstorder interpretations that input and output trees of bounded height. The corresponding functions have polynomial output size, since a firstorder interpretation can use a $k$tuple …

Oct. 4, 2023, 2:15 p.m.
Filip Mazowiecki (University of Warsaw)
Coverability in VASS Revisited: Improving Rackoff’s Bound to Obtain Conditional Optimality
Seminal results establish that the coverability problem for Vector Addition Systems with States (VASS) is in EXPSPACE (Rackoff, '78) and is EXPSPACEhard already under unary encodings (Lipton, '76). More precisely, Rosier and Yen later utilise …

Sept. 6, 2023, 2:15 p.m.
Uli Fahrenberg ( EPITA Rennes & Paris)
Higherdimensional automata theory
I will give a gentle introduction to higherdimensional automata (HDAs) and their language theory. HDAs have been introduced some 30 years ago as a model for noninterleaving concurrency which generalizes, for example, Petri nets while …