Lista referatów

• 2023-03-15, godz. 14:15, 5050

  Arka Ghosh (MIM UW)

  Orbit-finite systems of inequalities

  A system of inequalities is orbit-finite if it is finite up to certain permutations of variables. In this talk, I will describe this concept using interesting examples, and present our recent results on the solvability of these systems. In particular, we have proven that the existence of finitely su...

• 2023-03-08, godz. 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 lin...

• 2023-03-01, godz. 14:15, 5050

  Florent Koechlin (LORIA)

  Two criteria to prove the inherent ambiguity of bounded context-free languages

  A context-free 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 context-free language is a difficult problem, undecidable in general. The first examples of inherently ambigu...

• 2023-01-25, godz. 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, godz. 14:15, 5050

  Mikołaj Bojańczyk (MIM UW)

  TBA

• 2023-01-11, godz. 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, godz. 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, godz. 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, godz. 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, godz. 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...

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