Links' Seminars and Public Events | ![]() ![]() |
2022 | |
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Fri 1st Jul 11:00 am 12:00 pm | Séminaire Arnaud Durand |
Fri 10th Jun 10:00 am 11:00 am | Séminaire Corentin Barloy Title:The Regular Languages of First-Order Logic with One Alternation Abstract: The regular languages with a neutral letter expressible in first-order logic with one alternation are characterized. Specifically, it is shown that if an arbitrary Σ2 formula defines a regular language with a neutral letter, then there is an equivalent Σ2 formula that only uses the order predicate. This shows that the so-called Central Conjecture of Straubing holds for Σ2 over languages with a neutral letter, the first progress on the Conjecture in more than 20 years. To show the characterization, lower bounds against polynomial-size depth-3 Boolean circuits with constant top fan-in are developed. The heart of the combinatorial argument resides in studying how positions within a language are determined from one another, a technique of independent interest. |
Fri 25th Feb 11:00 am 12:00 pm | Séminaire Nico |
Fri 28th Jan 11:00 am 12:00 pm | Alexandre Vigny (visio) Title: Separator logic, expressive power and algorithmic applications Abstract: First-order logic (FO) can express many algorithmic problems on graphs, but fails to express whether two vertices are connected. We define a new logic (separator logic) by enriching FO with connectivity predicates connk(x, y, z1, . . . , zk) that hold true in a graph if there exists a path between x and y after deletion of z1, . . . , zk. In this talk I will first present a study of the expressive power of this new logic. I will then present algorithmic results for this logic on graph classes that exclude a topological minor. These results were obtained in collaboration with Michał Pilipczuk, Nicole Schirrmacher, Sebastian Siebertz, and Szymon Toruńczyk. |
Fri 21st Jan 11:00 am 12:00 pm | Aurélien Lemay in Seminar |