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

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 …

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 …