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

March 8, 2023, 2:15 p.m.
Michał Skrzypczak (MIM UW)
for contextfree 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 …

March 1, 2023, 2:15 p.m.
Florent Koechlin (LORIA)
Two criteria to prove the inherent ambiguity of bounded contextfree languages
A contextfree language is inherently ambiguous if any grammar recognizing it is ambiguous, i.e. there is a word that is generated in two different ways. Deciding the inherent ambiguity of a contextfree language is a …

Jan. 25, 2023, 2:15 p.m.
Hugo Gimbert (CNRS, LaBRI, Université de Bordeaux)
Martin’s proof of Borel determinacy
Donald Martin established Borel determinacy in 1975: in every GaleStewart 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 (bottomup …


Jan. 11, 2023, 2:15 p.m.
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 …

Dec. 21, 2022, 2:15 p.m.
Marcin Przybyłko (University of Leipzig)
Enumerating Answers to Ontology Mediated Queries
A known dichotomy states that for conjunctive queries (CQs) with no selfjoins the set of answers can be enumerated with linear preprocessing* and constant delay* if and only** if the query is both acyclic and …

Dec. 14, 2022, 2:15 p.m.
Antonio Casares Santos (LaBRI, Université de Bordeaux)
A correspondence between memory and automata for Muller languages
In this talk, we will be interested in infiniteduration 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. …

Dec. 7, 2022, 2:15 p.m.
Lorenzo Clemente (MIM UW)
Decidability of equivalence of deterministic oneway 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 …

Nov. 30, 2022, 2:15 p.m.
David Purser (MIM UW)
The bigO problem for maxplus automata
Given two weighted automata A and B over the (N, max, plus) semiring we consider the problem of deciding whether there exists a constant c such that A(w) ≤ c B(w) + c for every …

Nov. 23, 2022, 2:15 p.m.
Jakob Piribauer (TU Dresden)
Tradeoff between expectation and variance in Markov decision processes
The stochastic shortest path problem asks to resolve the nondeterministic choices in a Markov decision process (MDP) such that the expected accumulated weight before reaching a target state is maximized. This problem is wellstudied and …

Nov. 16, 2022, 2:15 p.m.
Mikołaj Bojańczyk (MIM UW)
Folding interpretations
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 …

Nov. 9, 2022, 2:15 p.m.
Paweł Parys (MIM UW)
Weak Bisimulation Finiteness of Pushdown Systems With Deterministic εTransitions Is 2EXPTIMEComplete
We consider the problem of deciding whether a given pushdown system all of whose εtransitions are deterministic is weakly bisimulation finite, that is, whether it is weakly bisimulation equivalent to a finite system. We prove …

Oct. 26, 2022, 2:15 p.m.
Michael Blondin (Université de Sherbrooke)
Separators in continuous Petri nets
In this talk, we will consider Petri nets: a wellestablished formalism for the analysis of concurrent systems. Testing whether a target Petri net configuration cannot be reached often amounts to proving the absence of bugs …

Oct. 19, 2022, 2:15 p.m.
Szymon Toruńczyk (MIM UW)
On monadically stable and monadically NIP classes of graphs
Sparsity theory, initiated by Ossona de Mendez and Nesetril, identifies those classes of sparse graphs that are tractable in various ways (e.g. from the perspective of the model checking problem for first order logic) as …

Oct. 11, 2022, 2:15 p.m.
Stefan Göller (Universität Kassel)
The AC0complexity of visibly pushdown languages.
The talk will be on the question which visibly pushdown languages (VPLs) are in the complexity class AC0. We provide a conjectural characterization that isolates a stubborn subclass of very particular oneturn visibly pushdown languages …