Organizers

prof. dr hab. Mikołaj Bojańczyk
prof. dr hab. Damian Niwiński

Information

Wednesdays, 2:15 p.m. , room: 5440

Research fields

List of talks

Dec. 6, 2023, 2:15 p.m.
Antonio Casares (University of Warsaw)
A characterization of half-positionality for omega-regular 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 omega-regular 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 well-known 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 (Polish-Japanese Academy of Information Technology)
Some remarks on Stone-Čech compactification in ZFA
Working in Zermelo-Fraenkel Set Theory with Atoms over an \omega-categorical \omega-stable structure, we show how some infinite constructions over definable sets can be encoded as finite constructions over Stone-Čech 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 structure-preserving 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 first-order interpretations that input and output trees of bounded height. The corresponding functions have polynomial output size, since a first-order 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 EXPSPACE-hard 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)
Higher-dimensional automata theory
I will give a gentle introduction to higher-dimensional automata (HDAs) and their language theory. HDAs have been introduced some 30 years ago as a model for non-interleaving concurrency which generalizes, for example, Petri nets while …
July 5, 2023, 2:15 p.m.
Michał Gajda (MigaMake Pte Ltd, Singapur)
Semigroup decomposition and semigroup transformers
Krohn-Rhodes 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 context-free grammars
I'll discuss algorithms for sampling and enumerating terms from a given probabilistic context-free 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)
Flip-width
I will define a new graph parameter called flip-width. Graph classes of bounded flip-width include classes of bounded expansion of Nesetril and Ossona de Mendez, as well as classes of bounded twin-width 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 string-to-string functions, i.e. functions that are recognized by copyless streaming string transducers, or any of their equivalent models, such as deterministic two-way automata. Although this class of functions is clearly important, …