Weekly research seminar

2023-09-06, 14:15, 5050

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 retaining some automata-theoretic intuition. They have been stud...

2023-07-05, 14:15, 5050

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, and is rather hard to follow in its full grace (over hundred pag...

2023-06-21, 14:15, 5050

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 such statements is true for all collections of discrete finite-valued rand...

2023-06-14, 14:15, 5050

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 talk about our recent contributions....

2023-06-07, 14:15, 5050

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 objective is positional over arbitrary arenas, and that the mean-payoff objective is po...

2023-05-31, 14:15, 5050

Szymon Toruńczyk (MIM UW)

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, Thomasse, and Watrigant....

2023-05-24, 14:15, 5050

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, in particular because of the many equi...

2023-05-17, 14:15, 5050

Liat Peterfreund (CNRS, LIGM, Paris-Est University)

**Querying incomplete numerical data: between certain and possible answers**Queries with aggregation and arithmetic operations, as well as incomplete data, are common in real-world databases, but we lack a good understanding of how they should interact. On the one hand, systems based on SQL provide ad-hoc rules for numerical nulls, on the other, theoretical research largely...

2023-05-10, 14:15, 5050

Nikolas Mählmann (University of Bremen)

**Monadically Stable Classes of Graphs**Intuitively, a class of graphs is monadically stable if first-order 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 as planarity, bounded treewidth, bounded degree, ...

2023-04-26, 14:15, 5050

Yoàv Montacute (University of Cambridge)

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 will provide an introduction to this topic and its extension to ...