Organizers

prof. dr hab. Mikołaj Bojańczyk
prof. dr hab. Damian Niwiński

Information

Wednesdays, 2:15 p.m. , room: 5050

Research fields

List of talks

June 16, 2021, 2:15 p.m.
Lê Thành Dũng (Tito) Nguyễn (LIPN (Paris Nord))
Comparison-free polyregular functions
We introduce a new automata-theoretic class of string-to-string functions with polynomial growth. Several equivalent definitions are provided: a machine model which is a restricted variant of pebble transducers, and a few inductive definitions that close …
June 9, 2021, 2:15 p.m.
Amina Doumane (CNRS-ENS Lyon)
Regular expressions for languages of graphs of tree-width 2
I propose a syntax of regular expressions which capture exactly CMSO definable languages of graphs of tree-width 2. A similar syntax is given for CMSO definable languages of series-parallel graphs and of connected tree-width 2 …
June 2, 2021, 2:15 p.m.
Gaëtan Douéneau (IRIF, Université de Paris)
Pebble transducers with unary output
Bojańczyk recently initiated an intensive study of deterministic pebble transducers, which are two-way automata that can drop marks (named "pebbles") on their input word, and produce an output word. They describe functions from words to …
May 26, 2021, 2:15 p.m.
Sandra Kiefer (MIM UW)
Logarithmic Weisfeiler-Leman Identifies All Planar Graphs
The Weisfeiler-Leman (WL) algorithm is a well-known combinatorial procedure for detecting symmetries in graphs that is widely used in graph-isomorphism tests. It proceeds by iteratively computing vertex colours. The number of iterations needed to obtain …
May 19, 2021, 2:15 p.m.
Jan Dreier (TU Wien, Austria)
Lacon- and Shrub-Decompositions: A New Characterization of First-Order Transductions of Bounded Expansion Classes
The concept of bounded expansion provides a robust way to capture sparse graph classes with interesting algorithmic properties. Most notably, every problem definable in first-order logic can be solved in linear time on bounded expansion …
May 12, 2021, 2:15 p.m.
Wojciech Czerwiński (MIM UW)
Reachability in Vector Addition Systems is Ackermann-complete
Complexity of the reachability problem in Vector Addition Systems (VASes) was a long standing problem for a few decades. Very recently two proofs of Ackermann-hardness were obtained independently (one by Jerome Leroux, one by us). …
May 5, 2021, 2:15 p.m.
Mikołaj Bojańczyk (MIM UW)
Star-free expressions for graphs, and an appropriate first-order logic
In the study of word languages, first-order logic is more frequently used with the order predicate x > y, and not the successor predicate x=y+1. (For MSO, there is no difference.) For example, the celebrated …
April 28, 2021, 2:15 p.m.
Nathanaël Fijalkow (LaBRI)
The theory of universal graphs for infinite duration games
2017 was a special year in the world of parity games. Now that the dust has settled, what have we learned from the new quasi polynomial algorithms? In this talk I'll introduce the notion of …
April 21, 2021, 2:15 p.m.
Lorenzo Clemente & Michał Skrzypczak (MIM UW & MIM UW)
Deterministic and game separability of tree languages via games
We show that it is decidable whether two regular languages of infinite trees are separable by a deterministic language, resp., a game language. We consider two variants of separability, depending on whether the set of …
April 14, 2021, 2:15 p.m.
Jakub Różycki (MIM UW)
On the expressiveness of Büchi arithmetic
Büchi arithmetic is a logical theory that is important for us, because it is equivalent to regular languages. We show that the existential fragment of Büchi arithmetic is strictly less expressive than full Büchi arithmetic …
March 31, 2021, 2:15 p.m.
Sandra Kiefer (MIM UW)
Decomposing and Identifying Graphs with Weisfeiler and Leman
The Weisfeiler-Leman (WL) procedure is a widely-used approach for graph-isomorphism testing. It works by iteratively computing an isomorphism-invariant coloring of vertex tuples. Meanwhile, decompositions are a fundamental tool in structural graph theory and often exploited …
March 31, 2021, 2:15 p.m.
Nathan Lhote (AIx-Marseille University)
Computability of Data-Word Transductions over Atoms
We investigate the problem of synthesizing computable functions of infinite words over an infinite alphabet (data ω-words). The notion of computability is defined through Turing machines with infinite inputs which can produce the corresponding infinite …
March 17, 2021, 2:15 p.m.
Mohnish Pattathurajan (MIM UW)
Parikh’s theorem for infinite alphabets
We investigate commutative images (Parikh Images) of languages recognised by register automata and grammars. Semi-linear and rational sets can be naturally extended to this setting by allowing for orbit-finite unions instead of finite ones. We …
March 10, 2021, 2:15 p.m.
Pierre Ohlmann (IRIF, Université de Paris)
Controlling a random population
Bertrand et al. introduced a model of parameterised systems, where each agent is represented by a finite state system, and studied the following control problem: for any number of agents, does there exist a controller …
March 3, 2021, 2:15 p.m.
Szymon Toruńczyk (MIM UW)
Ordered graphs of bounded twin-width
We consider hereditary classes of graphs equipped with a total order. We provide multiple equivalent characterisations of those classes which have bounded twin-width. In particular, we prove that those are exactly the classes which avoid …