Weekly research seminar

2023-01-25, 14:15, 5050

Hugo Gimbert (CNRS, LaBRI, Université de Bordeaux)

**Martin’s proof of Borel determinacy**Donald Martin established Borel determinacy in 1975: in every Gale-Stewart game with a Borel winning condition, either player I or player II has a winning strategy. We present Martin’s proof under a different perspective (bottom-up instead of top-down), in the special case where the winning condi...

2023-01-18, 14:15, 5050

Michał Skrzypczak (MIM UW)

**Binary counting is hard (for context-free grammars)**Michaël Cadilhac recently (on Autoboz) asked the following problem: Take n > 0 and consider the alphabet A_n = { 2^i | i ≤ n }. Let L_n be the set of words over A_n that sum up to 2^n. What is the size of the minimal context-free grammar which recognises L_n? The problem is motivated by l...

2023-01-11, 14:15, 5050

Pierre Ohlmann (MIM UW)

**Memory in games and universal graphs**I will present recent characterisations of positionality and finite memory in infinite duration games by means of universal graphs. The goal is to derive properties of games with a given objective W by understanding the structure of graphs satisfying W (meaning that all path colorations belong to W)...

2022-12-21, 14:15, 5050

Marcin Przybyłko (University of Leipzig)

**Enumerating Answers to Ontology Mediated Queries**A known dichotomy states that for conjunctive queries (CQs) with no self-joins the set of answers can be enumerated with linear preprocessing* and constant delay* if and only** if the query is both acyclic and free-connex. I will show how to lift those results to the enumeration of certain answer...

2022-12-14, 14:15, 5050

Antonio Casares Santos (LaBRI, Université de Bordeaux)

**A correspondence between memory and automata for Muller languages**In this talk, we will be interested in infinite-duration games using Muller winning conditions, that is, the objective of such games is given by a boolean combination of colors that have to appear infinitely often. In Muller games, finite memory strategies suffice, meaning that Eve can play optimall...

2022-12-07, 14:15, 5050

Lorenzo Clemente (MIM UW)

**Decidability of equivalence of deterministic one-way multitape finite automata**I will present an old decidability result by Harju and Karhumäki, as in the title. The original proof involves some very nice algebraic constructions, which constitute the motivation for this presentation. We start from the well-known problem of deciding equivalence of one-dimensional linear recu...

2022-11-30, 14:15, 5050

David Purser (MIM UW)

**The big-O problem for max-plus automata**Given two weighted automata A and B over the (N, max, plus) semi-ring we consider the problem of deciding whether there exists a constant c such that A(w) ≤ c B(w) + c for every word w. The problem is known as the big-O problem or affine domination. The problem is a relaxation of the containment p...

2022-11-23, 14:15, 5050

Jakob Piribauer (TU Dresden)

**Tradeoff between expectation and variance in Markov decision processes**The stochastic shortest path problem asks to resolve the non-deterministic choices in a Markov decision process (MDP) such that the expected accumulated weight before reaching a target state is maximized. This problem is well-studied and solvable in polynomial time. An optimal strategy might, howeve...

2022-11-16, 14:15, 5050

Mikołaj Bojańczyk (MIM UW)

In this talk, I will discuss a characterisation of the polyregular functions which uses folding. The idea is to use the combinator approach, i.e. start with certain atomic functions (such as list concatenation) and apply certain combinators (such as function composition). However, we want one of the...

2022-11-09, 14:15, 5050

Paweł Parys (MIM UW)

We consider the problem of deciding whether a given pushdown system all of whose ε-transitions are deterministic is weakly bisimulation finite, that is, whether it is weakly bisimulation equivalent to a finite system. We prove that this problem is 2-EXPTIME-complete. This consists of three elem...