Document

**Published in:** LIPIcs, Volume 306, 49th International Symposium on Mathematical Foundations of Computer Science (MFCS 2024)

We revisit the work studying homomorphism preservation for first-order logic in sparse classes of structures initiated in [Atserias et al., JACM 2006] and [Dawar, JCSS 2010]. These established that first-order logic has the homomorphism preservation property in any sparse class that is monotone and addable. It turns out that the assumption of addability is not strong enough for the proofs given. We demonstrate this by constructing classes of graphs of bounded treewidth which are monotone and addable but fail to have homomorphism preservation. We also show that homomorphism preservation fails on the class of planar graphs. On the other hand, the proofs of homomorphism preservation can be recovered by replacing addability by a stronger condition of amalgamation over bottlenecks. This is analogous to a similar condition formulated for extension preservation in [Atserias et al., SiCOMP 2008].

Anuj Dawar and Ioannis Eleftheriadis. Preservation Theorems on Sparse Classes Revisited. In 49th International Symposium on Mathematical Foundations of Computer Science (MFCS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 306, pp. 47:1-47:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{dawar_et_al:LIPIcs.MFCS.2024.47, author = {Dawar, Anuj and Eleftheriadis, Ioannis}, title = {{Preservation Theorems on Sparse Classes Revisited}}, booktitle = {49th International Symposium on Mathematical Foundations of Computer Science (MFCS 2024)}, pages = {47:1--47:16}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-335-5}, ISSN = {1868-8969}, year = {2024}, volume = {306}, editor = {Kr\'{a}lovi\v{c}, Rastislav and Ku\v{c}era, Anton{\'\i}n}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2024.47}, URN = {urn:nbn:de:0030-drops-206036}, doi = {10.4230/LIPIcs.MFCS.2024.47}, annote = {Keywords: Homomorphism preservation, sparsity, finite model theory, planar graphs} }

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Invited Talk

**Published in:** LIPIcs, Volume 297, 51st International Colloquium on Automata, Languages, and Programming (ICALP 2024)

I survey recent work on symmetric computation. A number of strands of work, from logic, circuit complexity, combinatorial optimization and other areas have converged on similar notions of symmetry in computation. This write-up of an invited talk gives a whirlwind tour through the results and pointers to the relevant literature.

Anuj Dawar. Limits of Symmetric Computation (Invited Talk). In 51st International Colloquium on Automata, Languages, and Programming (ICALP 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 297, pp. 1:1-1:8, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{dawar:LIPIcs.ICALP.2024.1, author = {Dawar, Anuj}, title = {{Limits of Symmetric Computation}}, booktitle = {51st International Colloquium on Automata, Languages, and Programming (ICALP 2024)}, pages = {1:1--1:8}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-322-5}, ISSN = {1868-8969}, year = {2024}, volume = {297}, editor = {Bringmann, Karl and Grohe, Martin and Puppis, Gabriele and Svensson, Ola}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2024.1}, URN = {urn:nbn:de:0030-drops-201444}, doi = {10.4230/LIPIcs.ICALP.2024.1}, annote = {Keywords: Logic, Complexity Theory, Symmetric Computation} }

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**Published in:** LIPIcs, Volume 288, 32nd EACSL Annual Conference on Computer Science Logic (CSL 2024)

We study Lindström quantifiers that satisfy certain closure properties which are motivated by the study of polymorphisms in the context of constraint satisfaction problems (CSP). When the algebra of polymorphisms of a finite structure 𝔅 satisfies certain equations, this gives rise to a natural closure condition on the class of structures that map homomorphically to 𝔅. The collection of quantifiers that satisfy closure conditions arising from a fixed set of equations are rather more general than those arising as CSP. For any such conditions 𝒫, we define a pebble game that delimits the distinguishing power of the infinitary logic with all quantifiers that are 𝒫-closed. We use the pebble game to show that the problem of deciding whether a system of linear equations is solvable in ℤ / 2ℤ is not expressible in the infinitary logic with all quantifiers closed under a near-unanimity condition.

Anuj Dawar and Lauri Hella. Quantifiers Closed Under Partial Polymorphisms. In 32nd EACSL Annual Conference on Computer Science Logic (CSL 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 288, pp. 23:1-23:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{dawar_et_al:LIPIcs.CSL.2024.23, author = {Dawar, Anuj and Hella, Lauri}, title = {{Quantifiers Closed Under Partial Polymorphisms}}, booktitle = {32nd EACSL Annual Conference on Computer Science Logic (CSL 2024)}, pages = {23:1--23:19}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-310-2}, ISSN = {1868-8969}, year = {2024}, volume = {288}, editor = {Murano, Aniello and Silva, Alexandra}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2024.23}, URN = {urn:nbn:de:0030-drops-196662}, doi = {10.4230/LIPIcs.CSL.2024.23}, annote = {Keywords: generalized quantifiers, constraint satisfaction problems, pebble games, finite variable logics, descriptive complexity theory} }

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Track B: Automata, Logic, Semantics, and Theory of Programming

**Published in:** LIPIcs, Volume 261, 50th International Colloquium on Automata, Languages, and Programming (ICALP 2023)

We prove that for any monotone class of finite relational structures, the first-order theory of the class is NIP in the sense of stability theory if, and only if, the collection of Gaifman graphs of structures in this class is nowhere dense. This generalises results previously known for graphs to relational structures and answers an open question posed by Adler and Adler (2014). The result is established by the application of Ramsey-theoretic techniques and shows that the property of being NIP is highly robust for monotone classes. We also show that the model-checking problem for first-order logic is intractable on any monotone class of structures that is not (monadically) NIP. This is a contribution towards the conjecture that the hereditary classes of structures admitting fixed-parameter tractable model-checking are precisely those that are monadically NIP.

Samuel Braunfeld, Anuj Dawar, Ioannis Eleftheriadis, and Aris Papadopoulos. Monadic NIP in Monotone Classes of Relational Structures. In 50th International Colloquium on Automata, Languages, and Programming (ICALP 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 261, pp. 119:1-119:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{braunfeld_et_al:LIPIcs.ICALP.2023.119, author = {Braunfeld, Samuel and Dawar, Anuj and Eleftheriadis, Ioannis and Papadopoulos, Aris}, title = {{Monadic NIP in Monotone Classes of Relational Structures}}, booktitle = {50th International Colloquium on Automata, Languages, and Programming (ICALP 2023)}, pages = {119:1--119:18}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-278-5}, ISSN = {1868-8969}, year = {2023}, volume = {261}, editor = {Etessami, Kousha and Feige, Uriel and Puppis, Gabriele}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2023.119}, URN = {urn:nbn:de:0030-drops-181712}, doi = {10.4230/LIPIcs.ICALP.2023.119}, annote = {Keywords: Model theory, finite model theory, structural graph theory, model-checking} }

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Complete Volume

**Published in:** LIPIcs, Volume 254, 40th International Symposium on Theoretical Aspects of Computer Science (STACS 2023)

LIPIcs, Volume 254, STACS 2023, Complete Volume

40th International Symposium on Theoretical Aspects of Computer Science (STACS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 254, pp. 1-1026, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@Proceedings{berenbrink_et_al:LIPIcs.STACS.2023, title = {{LIPIcs, Volume 254, STACS 2023, Complete Volume}}, booktitle = {40th International Symposium on Theoretical Aspects of Computer Science (STACS 2023)}, pages = {1--1026}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-266-2}, ISSN = {1868-8969}, year = {2023}, volume = {254}, editor = {Berenbrink, Petra and Bouyer, Patricia and Dawar, Anuj and Kant\'{e}, Mamadou Moustapha}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2023}, URN = {urn:nbn:de:0030-drops-176515}, doi = {10.4230/LIPIcs.STACS.2023}, annote = {Keywords: LIPIcs, Volume 254, STACS 2023, Complete Volume} }

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Front Matter

**Published in:** LIPIcs, Volume 254, 40th International Symposium on Theoretical Aspects of Computer Science (STACS 2023)

Front Matter, Table of Contents, Preface, Conference Organization

40th International Symposium on Theoretical Aspects of Computer Science (STACS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 254, pp. 0:i-0:xxii, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{berenbrink_et_al:LIPIcs.STACS.2023.0, author = {Berenbrink, Petra and Bouyer, Patricia and Dawar, Anuj and Kant\'{e}, Mamadou Moustapha}, title = {{Front Matter, Table of Contents, Preface, Conference Organization}}, booktitle = {40th International Symposium on Theoretical Aspects of Computer Science (STACS 2023)}, pages = {0:i--0:xxii}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-266-2}, ISSN = {1868-8969}, year = {2023}, volume = {254}, editor = {Berenbrink, Petra and Bouyer, Patricia and Dawar, Anuj and Kant\'{e}, Mamadou Moustapha}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2023.0}, URN = {urn:nbn:de:0030-drops-176525}, doi = {10.4230/LIPIcs.STACS.2023.0}, annote = {Keywords: Front Matter, Table of Contents, Preface, Conference Organization} }

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Complete Volume

**Published in:** LIPIcs, Volume 250, 42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022)

LIPIcs, Volume 250, FSTTCS 2022, Complete Volume

42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 250, pp. 1-792, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@Proceedings{dawar_et_al:LIPIcs.FSTTCS.2022, title = {{LIPIcs, Volume 250, FSTTCS 2022, Complete Volume}}, booktitle = {42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022)}, pages = {1--792}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-261-7}, ISSN = {1868-8969}, year = {2022}, volume = {250}, editor = {Dawar, Anuj and Guruswami, Venkatesan}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2022}, URN = {urn:nbn:de:0030-drops-173910}, doi = {10.4230/LIPIcs.FSTTCS.2022}, annote = {Keywords: LIPIcs, Volume 250, FSTTCS 2022, Complete Volume} }

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Front Matter

**Published in:** LIPIcs, Volume 250, 42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022)

Front Matter, Table of Contents, Preface, Conference Organization

42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 250, pp. 0:i-0:xvi, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{dawar_et_al:LIPIcs.FSTTCS.2022.0, author = {Dawar, Anuj and Guruswami, Venkatesan}, title = {{Front Matter, Table of Contents, Preface, Conference Organization}}, booktitle = {42nd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2022)}, pages = {0:i--0:xvi}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-261-7}, ISSN = {1868-8969}, year = {2022}, volume = {250}, editor = {Dawar, Anuj and Guruswami, Venkatesan}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2022.0}, URN = {urn:nbn:de:0030-drops-173928}, doi = {10.4230/LIPIcs.FSTTCS.2022.0}, annote = {Keywords: Front Matter, Table of Contents, Preface, Conference Organization} }

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**Published in:** LIPIcs, Volume 216, 30th EACSL Annual Conference on Computer Science Logic (CSL 2022)

Seese’s conjecture for finite graphs states that monadic second-order logic (MSO) is undecidable on all graph classes of unbounded clique-width. We show that to establish this it would suffice to show that grids of unbounded size can be interpreted in two families of graph classes: minimal hereditary classes of unbounded clique-width; and antichains of unbounded clique-width under the induced subgraph relation. We explore all the currently known classes of the former category and establish that grids of unbounded size can indeed be interpreted in them.

Anuj Dawar and Abhisekh Sankaran. MSO Undecidability for Hereditary Classes of Unbounded Clique Width. In 30th EACSL Annual Conference on Computer Science Logic (CSL 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 216, pp. 17:1-17:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{dawar_et_al:LIPIcs.CSL.2022.17, author = {Dawar, Anuj and Sankaran, Abhisekh}, title = {{MSO Undecidability for Hereditary Classes of Unbounded Clique Width}}, booktitle = {30th EACSL Annual Conference on Computer Science Logic (CSL 2022)}, pages = {17:1--17:17}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-218-1}, ISSN = {1868-8969}, year = {2022}, volume = {216}, editor = {Manea, Florin and Simpson, Alex}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2022.17}, URN = {urn:nbn:de:0030-drops-157373}, doi = {10.4230/LIPIcs.CSL.2022.17}, annote = {Keywords: clique width, Seese’s conjecture, antichain, MSO interpretation, grid} }

Document

**Published in:** LIPIcs, Volume 215, 13th Innovations in Theoretical Computer Science Conference (ITCS 2022)

Dawar and Wilsenach (ICALP 2020) introduce the model of symmetric arithmetic circuits and show an exponential separation between the sizes of symmetric circuits for computing the determinant and the permanent. The symmetry restriction is that the circuits which take a matrix input are unchanged by a permutation applied simultaneously to the rows and columns of the matrix. Under such restrictions we have polynomial-size circuits for computing the determinant but no subexponential size circuits for the permanent. Here, we consider a more stringent symmetry requirement, namely that the circuits are unchanged by arbitrary even permutations applied separately to rows and columns, and prove an exponential lower bound even for circuits computing the determinant. The result requires substantial new machinery. We develop a general framework for proving lower bounds for symmetric circuits with restricted symmetries, based on a new support theorem and new two-player restricted bijection games. These are applied to the determinant problem with a novel construction of matrices that are bi-adjacency matrices of graphs based on the CFI construction. Our general framework opens the way to exploring a variety of symmetry restrictions and studying trade-offs between symmetry and other resources used by arithmetic circuits.

Anuj Dawar and Gregory Wilsenach. Lower Bounds for Symmetric Circuits for the Determinant. In 13th Innovations in Theoretical Computer Science Conference (ITCS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 215, pp. 52:1-52:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{dawar_et_al:LIPIcs.ITCS.2022.52, author = {Dawar, Anuj and Wilsenach, Gregory}, title = {{Lower Bounds for Symmetric Circuits for the Determinant}}, booktitle = {13th Innovations in Theoretical Computer Science Conference (ITCS 2022)}, pages = {52:1--52:22}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-217-4}, ISSN = {1868-8969}, year = {2022}, volume = {215}, editor = {Braverman, Mark}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2022.52}, URN = {urn:nbn:de:0030-drops-156480}, doi = {10.4230/LIPIcs.ITCS.2022.52}, annote = {Keywords: arithmetic circuits, symmetric arithmetic circuits, Boolean circuits, symmetric circuits, permanent, determinant, counting width, Weisfeiler-Leman dimension, Cai-F\"{u}rer-Immerman constructions} }

Document

**Published in:** LIPIcs, Volume 202, 46th International Symposium on Mathematical Foundations of Computer Science (MFCS 2021)

We compare the capabilities of two approaches to approximating graph isomorphism using linear algebraic methods: the invertible map tests (introduced by Dawar and Holm) and proof systems with algebraic rules, namely polynomial calculus, monomial calculus and Nullstellensatz calculus. In the case of fields of characteristic zero, these variants are all essentially equivalent to the Weisfeiler-Leman algorithms. In positive characteristic we show that the distinguishing power of the monomial calculus is no greater than the invertible map method by simulating the former in a fixed-point logic with solvability operators. In turn, we show that the distinctions made by this logic can be implemented in the Nullstellensatz calculus.

Anuj Dawar and Danny Vagnozzi. On the Relative Power of Linear Algebraic Approximations of Graph Isomorphism. In 46th International Symposium on Mathematical Foundations of Computer Science (MFCS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 202, pp. 37:1-37:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{dawar_et_al:LIPIcs.MFCS.2021.37, author = {Dawar, Anuj and Vagnozzi, Danny}, title = {{On the Relative Power of Linear Algebraic Approximations of Graph Isomorphism}}, booktitle = {46th International Symposium on Mathematical Foundations of Computer Science (MFCS 2021)}, pages = {37:1--37:16}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-201-3}, ISSN = {1868-8969}, year = {2021}, volume = {202}, editor = {Bonchi, Filippo and Puglisi, Simon J.}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2021.37}, URN = {urn:nbn:de:0030-drops-144774}, doi = {10.4230/LIPIcs.MFCS.2021.37}, annote = {Keywords: Graph isomorphism, proof complexity, invertible map tests} }

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**Published in:** LIPIcs, Volume 183, 29th EACSL Annual Conference on Computer Science Logic (CSL 2021)

Game comonads, introduced by Abramsky, Dawar and Wang and developed by Abramsky and Shah, give an interesting categorical semantics to some Spoiler-Duplicator games that are common in finite model theory. In particular they expose connections between one-sided and two-sided games, and parameters such as treewidth and treedepth and corresponding notions of decomposition. In the present paper, we expand the realm of game comonads to logics with generalised quantifiers. In particular, we introduce a comonad graded by two parameter n ≤ k such that isomorphisms in the resulting Kleisli category are exactly Duplicator winning strategies in Hella’s n-bijection game with k pebbles. We define a one-sided version of this game which allows us to provide a categorical semantics for a number of logics with generalised quantifiers. We also give a novel notion of tree decomposition that emerges from the construction.

Adam Ó Conghaile and Anuj Dawar. Game Comonads & Generalised Quantifiers. In 29th EACSL Annual Conference on Computer Science Logic (CSL 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 183, pp. 16:1-16:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{conghaile_et_al:LIPIcs.CSL.2021.16, author = {Conghaile, Adam \'{O} and Dawar, Anuj}, title = {{Game Comonads \& Generalised Quantifiers}}, booktitle = {29th EACSL Annual Conference on Computer Science Logic (CSL 2021)}, pages = {16:1--16:17}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-175-7}, ISSN = {1868-8969}, year = {2021}, volume = {183}, editor = {Baier, Christel and Goubault-Larrecq, Jean}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2021.16}, URN = {urn:nbn:de:0030-drops-134501}, doi = {10.4230/LIPIcs.CSL.2021.16}, annote = {Keywords: Logic, Finite Model Theory, Game Comonads, Generalised Quantifiers} }

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**Published in:** LIPIcs, Volume 183, 29th EACSL Annual Conference on Computer Science Logic (CSL 2021)

It is well known that the classic Łoś-Tarski preservation theorem fails in the finite: there are first-order definable classes of finite structures closed under extensions which are not definable (in the finite) in the existential fragment of first-order logic. We strengthen this by constructing for every n, first-order definable classes of finite structures closed under extensions which are not definable with n quantifier alternations. The classes we construct are definable in the extension of Datalog with negation and indeed in the existential fragment of transitive-closure logic. This answers negatively an open question posed by Rosen and Weinstein.

Anuj Dawar and Abhisekh Sankaran. Extension Preservation in the Finite and Prefix Classes of First Order Logic. In 29th EACSL Annual Conference on Computer Science Logic (CSL 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 183, pp. 18:1-18:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{dawar_et_al:LIPIcs.CSL.2021.18, author = {Dawar, Anuj and Sankaran, Abhisekh}, title = {{Extension Preservation in the Finite and Prefix Classes of First Order Logic}}, booktitle = {29th EACSL Annual Conference on Computer Science Logic (CSL 2021)}, pages = {18:1--18:13}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-175-7}, ISSN = {1868-8969}, year = {2021}, volume = {183}, editor = {Baier, Christel and Goubault-Larrecq, Jean}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2021.18}, URN = {urn:nbn:de:0030-drops-134520}, doi = {10.4230/LIPIcs.CSL.2021.18}, annote = {Keywords: finite model theory, preservation theorems, extension closed, composition, Datalog, Ehrenfeucht-Fraisse games} }

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Complete Volume

**Published in:** LIPIcs, Volume 168, 47th International Colloquium on Automata, Languages, and Programming (ICALP 2020)

LIPIcs, Volume 168, ICALP 2020, Complete Volume

47th International Colloquium on Automata, Languages, and Programming (ICALP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 168, pp. 1-2446, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@Proceedings{czumaj_et_al:LIPIcs.ICALP.2020, title = {{LIPIcs, Volume 168, ICALP 2020, Complete Volume}}, booktitle = {47th International Colloquium on Automata, Languages, and Programming (ICALP 2020)}, pages = {1--2446}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-138-2}, ISSN = {1868-8969}, year = {2020}, volume = {168}, editor = {Czumaj, Artur and Dawar, Anuj and Merelli, Emanuela}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2020}, URN = {urn:nbn:de:0030-drops-124067}, doi = {10.4230/LIPIcs.ICALP.2020}, annote = {Keywords: LIPIcs, Volume 168, ICALP 2020, Complete Volume} }

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Front Matter

**Published in:** LIPIcs, Volume 168, 47th International Colloquium on Automata, Languages, and Programming (ICALP 2020)

Front Matter, Table of Contents, Preface, Conference Organization

47th International Colloquium on Automata, Languages, and Programming (ICALP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 168, pp. 0:i-0:xxxvi, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{czumaj_et_al:LIPIcs.ICALP.2020.0, author = {Czumaj, Artur and Dawar, Anuj and Merelli, Emanuela}, title = {{Front Matter, Table of Contents, Preface, Conference Organization}}, booktitle = {47th International Colloquium on Automata, Languages, and Programming (ICALP 2020)}, pages = {0:i--0:xxxvi}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-138-2}, ISSN = {1868-8969}, year = {2020}, volume = {168}, editor = {Czumaj, Artur and Dawar, Anuj and Merelli, Emanuela}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2020.0}, URN = {urn:nbn:de:0030-drops-124075}, doi = {10.4230/LIPIcs.ICALP.2020.0}, annote = {Keywords: Front Matter, Table of Contents, Preface, Conference Organization} }

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Track A: Algorithms, Complexity and Games

**Published in:** LIPIcs, Volume 168, 47th International Colloquium on Automata, Languages, and Programming (ICALP 2020)

We introduce symmetric arithmetic circuits, i.e. arithmetic circuits with a natural symmetry restriction. In the context of circuits computing polynomials defined on a matrix of variables, such as the determinant or the permanent, the restriction amounts to requiring that the shape of the circuit is invariant under row and column permutations of the matrix. We establish unconditional, nearly exponential, lower bounds on the size of any symmetric circuit for computing the permanent over any field of characteristic other than 2. In contrast, we show that there are polynomial-size symmetric circuits for computing the determinant over fields of characteristic zero.

Anuj Dawar and Gregory Wilsenach. Symmetric Arithmetic Circuits. In 47th International Colloquium on Automata, Languages, and Programming (ICALP 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 168, pp. 36:1-36:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{dawar_et_al:LIPIcs.ICALP.2020.36, author = {Dawar, Anuj and Wilsenach, Gregory}, title = {{Symmetric Arithmetic Circuits}}, booktitle = {47th International Colloquium on Automata, Languages, and Programming (ICALP 2020)}, pages = {36:1--36:18}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-138-2}, ISSN = {1868-8969}, year = {2020}, volume = {168}, editor = {Czumaj, Artur and Dawar, Anuj and Merelli, Emanuela}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2020.36}, URN = {urn:nbn:de:0030-drops-124430}, doi = {10.4230/LIPIcs.ICALP.2020.36}, annote = {Keywords: arithmetic circuits, symmetric arithmetic circuits, Boolean circuits, symmetric circuits, permanent, determinant, counting width, Weisfeiler-Leman dimension, Cai-F\"{u}rer-Immerman constructions} }

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Invited Talk

**Published in:** LIPIcs, Volume 152, 28th EACSL Annual Conference on Computer Science Logic (CSL 2020)

We discuss a recent convergence of notions of symmetric computation arising in the theory of linear programming, in logic and in circuit complexity. This leads us to a coherent and robust definition of problems that are efficiently and symmetrically solvable. This is at once a rich class of problems and one for which we have methods for proving lower bounds. In this paper, we take a tour through results which show applications of these methods in a number of areas.

Anuj Dawar. Symmetric Computation (Invited Talk). In 28th EACSL Annual Conference on Computer Science Logic (CSL 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 152, pp. 2:1-2:12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{dawar:LIPIcs.CSL.2020.2, author = {Dawar, Anuj}, title = {{Symmetric Computation}}, booktitle = {28th EACSL Annual Conference on Computer Science Logic (CSL 2020)}, pages = {2:1--2:12}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-132-0}, ISSN = {1868-8969}, year = {2020}, volume = {152}, editor = {Fern\'{a}ndez, Maribel and Muscholl, Anca}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2020.2}, URN = {urn:nbn:de:0030-drops-116455}, doi = {10.4230/LIPIcs.CSL.2020.2}, annote = {Keywords: Descriptive Complexity, Fixed-point Logic with Counting, Circuit Complexity, Linear Programming, Hardness of Approximation, Arithmetic Circuits} }

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Track B: Automata, Logic, Semantics, and Theory of Programming

**Published in:** LIPIcs, Volume 132, 46th International Colloquium on Automata, Languages, and Programming (ICALP 2019)

Invertible map equivalences are approximations of graph isomorphism that refine the well-known Weisfeiler-Leman method. They are parameterized by a number k and a set Q of primes. The intuition is that two equivalent graphs G equiv^IM_{k, Q} H cannot be distinguished by means of partitioning the set of k-tuples in both graphs with respect to any linear-algebraic operator acting on vector spaces over fields of characteristic p, for any p in Q. These equivalences have first appeared in the study of rank logic, but in fact they can be used to delimit the expressive power of any extension of fixed-point logic with linear-algebraic operators. We define {LA^{k}}(Q), an infinitary logic with k variables and all linear-algebraic operators over finite vector spaces of characteristic p in Q and show that equiv^IM_{k, Q} is the natural notion of elementary equivalence for this logic. The logic LA^{omega}(Q) = Cup_{k in omega} LA^{k}(Q) is then a natural upper bound on the expressive power of any extension of fixed-point logics by means of Q-linear-algebraic operators.
By means of a new and much deeper algebraic analysis of a generalized variant, for any prime p, of the CFI-structures due to Cai, Fürer, and Immerman, we prove that, as long as Q is not the set of all primes, there is no k such that equiv^IM_{k, Q} is the same as isomorphism. It follows that there are polynomial-time properties of graphs which are not definable in LA^{omega}(Q), which implies that no extension of fixed-point logic with linear-algebraic operators can capture PTIME, unless it includes such operators for all prime characteristics. Our analysis requires substantial algebraic machinery, including a homogeneity property of CFI-structures and Maschke’s Theorem, an important result from the representation theory of finite groups.

Anuj Dawar, Erich Grädel, and Wied Pakusa. Approximations of Isomorphism and Logics with Linear-Algebraic Operators (Track B: Automata, Logic, Semantics, and Theory of Programming). In 46th International Colloquium on Automata, Languages, and Programming (ICALP 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 132, pp. 112:1-112:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{dawar_et_al:LIPIcs.ICALP.2019.112, author = {Dawar, Anuj and Gr\"{a}del, Erich and Pakusa, Wied}, title = {{Approximations of Isomorphism and Logics with Linear-Algebraic Operators}}, booktitle = {46th International Colloquium on Automata, Languages, and Programming (ICALP 2019)}, pages = {112:1--112:14}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-109-2}, ISSN = {1868-8969}, year = {2019}, volume = {132}, editor = {Baier, Christel and Chatzigiannakis, Ioannis and Flocchini, Paola and Leonardi, Stefano}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2019.112}, URN = {urn:nbn:de:0030-drops-106887}, doi = {10.4230/LIPIcs.ICALP.2019.112}, annote = {Keywords: Finite Model Theory, Graph Isomorphism, Descriptive Complexity, Algebra} }

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**Published in:** LIPIcs, Volume 119, 27th EACSL Annual Conference on Computer Science Logic (CSL 2018)

We consider the hardness of approximation of optimization problems from the point of view of definability. For many NP-hard optimization problems it is known that, unless P = NP, no polynomial-time algorithm can give an approximate solution guaranteed to be within a fixed constant factor of the optimum. We show, in several such instances and without any complexity theoretic assumption, that no algorithm that is expressible in fixed-point logic with counting (FPC) can compute an approximate solution. Since important algorithmic techniques for approximation algorithms (such as linear or semidefinite programming) are expressible in FPC, this yields lower bounds on what can be achieved by such methods. The results are established by showing lower bounds on the number of variables required in first-order logic with counting to separate instances with a high optimum from those with a low optimum for fixed-size instances.

Albert Atserias and Anuj Dawar. Definable Inapproximability: New Challenges for Duplicator. In 27th EACSL Annual Conference on Computer Science Logic (CSL 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 119, pp. 7:1-7:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{atserias_et_al:LIPIcs.CSL.2018.7, author = {Atserias, Albert and Dawar, Anuj}, title = {{Definable Inapproximability: New Challenges for Duplicator}}, booktitle = {27th EACSL Annual Conference on Computer Science Logic (CSL 2018)}, pages = {7:1--7:21}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-088-0}, ISSN = {1868-8969}, year = {2018}, volume = {119}, editor = {Ghica, Dan R. and Jung, Achim}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2018.7}, URN = {urn:nbn:de:0030-drops-96742}, doi = {10.4230/LIPIcs.CSL.2018.7}, annote = {Keywords: Descriptive Compleixty, Hardness of Approximation, MAX SAT, Vertex Cover, Fixed-point logic with counting} }

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**Published in:** LIPIcs, Volume 119, 27th EACSL Annual Conference on Computer Science Logic (CSL 2018)

Fixed-point logic with rank (FPR) is an extension of fixed-point logic with counting (FPC) with operators for computing the rank of a matrix over a finite field. The expressive power of FPR properly extends that of FPC and is contained in P, but it is not known if that containment is proper. We give a circuit characterization for FPR in terms of families of symmetric circuits with rank gates, along the lines of that for FPC given by [Anderson and Dawar 2017]. This requires the development of a broad framework of circuits in which the individual gates compute functions that are not symmetric (i.e., invariant under all permutations of their inputs). This framework also necessitates the development of novel techniques to prove the equivalence of circuits and logic. Both the framework and the techniques are of greater generality than the main result.

Anuj Dawar and Gregory Wilsenach. Symmetric Circuits for Rank Logic. In 27th EACSL Annual Conference on Computer Science Logic (CSL 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 119, pp. 20:1-20:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{dawar_et_al:LIPIcs.CSL.2018.20, author = {Dawar, Anuj and Wilsenach, Gregory}, title = {{Symmetric Circuits for Rank Logic}}, booktitle = {27th EACSL Annual Conference on Computer Science Logic (CSL 2018)}, pages = {20:1--20:16}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-088-0}, ISSN = {1868-8969}, year = {2018}, volume = {119}, editor = {Ghica, Dan R. and Jung, Achim}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2018.20}, URN = {urn:nbn:de:0030-drops-96870}, doi = {10.4230/LIPIcs.CSL.2018.20}, annote = {Keywords: fixed-point logic with rank, circuits, symmetric circuits, uniform families of circuits, circuit characterization, circuit framework, finite model theory, descriptive complexity} }

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**Published in:** Dagstuhl Reports, Volume 7, Issue 9 (2018)

This report documents the program and the outcomes of Dagstuhl Seminar 17361 "Finite and Algorithmic Model Theory".

Anuj Dawar, Erich Grädel, Phokion G. Kolaitis, and Thomas Schwentick. Finite and Algorithmic Model Theory (Dagstuhl Seminar 17361). In Dagstuhl Reports, Volume 7, Issue 9, pp. 1-25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Article{dawar_et_al:DagRep.7.9.1, author = {Dawar, Anuj and Gr\"{a}del, Erich and Kolaitis, Phokion G. and Schwentick, Thomas}, title = {{Finite and Algorithmic Model Theory (Dagstuhl Seminar 17361)}}, pages = {1--25}, journal = {Dagstuhl Reports}, ISSN = {2192-5283}, year = {2018}, volume = {7}, number = {9}, editor = {Dawar, Anuj and Gr\"{a}del, Erich and Kolaitis, Phokion G. and Schwentick, Thomas}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/DagRep.7.9.1}, URN = {urn:nbn:de:0030-drops-85863}, doi = {10.4230/DagRep.7.9.1}, annote = {Keywords: algorithms, database theory, descriptive complexity, finite model theory, independence logic, knowledge representation, model checking} }

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**Published in:** LIPIcs, Volume 82, 26th EACSL Annual Conference on Computer Science Logic (CSL 2017)

The Ackermann Award is the EACSL Outstanding Dissertation Award for Logic in Computer Science. It is presented during the annual conference of the EACSL (CSL'xx). This contribution reports on the 2017 edition of the award.

Anuj Dawar and Daniel Leivant. The Ackermann Award 2017. In 26th EACSL Annual Conference on Computer Science Logic (CSL 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 82, pp. 1:1-1:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{dawar_et_al:LIPIcs.CSL.2017.1, author = {Dawar, Anuj and Leivant, Daniel}, title = {{The Ackermann Award 2017}}, booktitle = {26th EACSL Annual Conference on Computer Science Logic (CSL 2017)}, pages = {1:1--1:4}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-045-3}, ISSN = {1868-8969}, year = {2017}, volume = {82}, editor = {Goranko, Valentin and Dam, Mads}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2017.1}, URN = {urn:nbn:de:0030-drops-76938}, doi = {10.4230/LIPIcs.CSL.2017.1}, annote = {Keywords: Ackermann Award, jury report, citation} }

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**Published in:** LIPIcs, Volume 62, 25th EACSL Annual Conference on Computer Science Logic (CSL 2016)

The Ackermann Award is the EACSL Outstanding Dissertation Award for Logic in Computer Science. It is presented during the annual conference of the EACSL (CSL'xx). This contribution reports on the 2016 edition of the award.

Thierry Coquand and Anuj Dawar. The Ackermann Award 2016. In 25th EACSL Annual Conference on Computer Science Logic (CSL 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 62, pp. 1:1-1:4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{coquand_et_al:LIPIcs.CSL.2016.1, author = {Coquand, Thierry and Dawar, Anuj}, title = {{The Ackermann Award 2016}}, booktitle = {25th EACSL Annual Conference on Computer Science Logic (CSL 2016)}, pages = {1:1--1:4}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-022-4}, ISSN = {1868-8969}, year = {2016}, volume = {62}, editor = {Talbot, Jean-Marc and Regnier, Laurent}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2016.1}, URN = {urn:nbn:de:0030-drops-65419}, doi = {10.4230/LIPIcs.CSL.2016.1}, annote = {Keywords: Ackermann Award, Computer Science, Logic} }

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**Published in:** Dagstuhl Reports, Volume 5, Issue 12 (2016)

This report documents the program and the outcomes of Dagstuhl Seminar 15511 "The Graph Isomorphism Problem". The goal of the seminar was to bring together researchers working on the numerous topics closely related to the
Isomorphism Problem to foster their collaboration. To this end the participants of the seminar included researchers working on the theoretical and practical aspects of isomorphism ranging from the fields of algorithmic group theory, finite model theory, combinatorial optimization to algorithmics.
A highlight of the conference was the presentation of a new quasi-polynomial time algorithm for the Graph Isomorphism Problem, providing the first improvement since 1983.

László Babai, Anuj Dawar, Pascal Schweitzer, and Jacobo Torán. The Graph Isomorphism Problem (Dagstuhl Seminar 15511). In Dagstuhl Reports, Volume 5, Issue 12, pp. 1-17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@Article{babai_et_al:DagRep.5.12.1, author = {Babai, L\'{a}szl\'{o} and Dawar, Anuj and Schweitzer, Pascal and Tor\'{a}n, Jacobo}, title = {{The Graph Isomorphism Problem (Dagstuhl Seminar 15511)}}, pages = {1--17}, journal = {Dagstuhl Reports}, ISSN = {2192-5283}, year = {2016}, volume = {5}, number = {12}, editor = {Babai, L\'{a}szl\'{o} and Dawar, Anuj and Schweitzer, Pascal and Tor\'{a}n, Jacobo}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/DagRep.5.12.1}, URN = {urn:nbn:de:0030-drops-58028}, doi = {10.4230/DagRep.5.12.1}, annote = {Keywords: canonical forms, complexity, computational group theory, graph isomorphism} }

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**Published in:** LIPIcs, Volume 43, 10th International Symposium on Parameterized and Exact Computation (IPEC 2015)

We show that for various classes C of sparse graphs, and several measures of distance to such classes (such as edit distance and elimination distance), the problem of determining the distance of a given graph G to C is fixed-parameter tractable. The results are based on two general techniques. The first of these, building on recent work of Grohe et al. establishes that any class of graphs that is slicewise nowhere dense and slicewise first-order definable is FPT. The second shows that determining the elimination distance of a graph G to a minor-closed class C is FPT.

Jannis Bulian and Anuj Dawar. Fixed-parameter Tractable Distances to Sparse Graph Classes. In 10th International Symposium on Parameterized and Exact Computation (IPEC 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 43, pp. 236-247, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{bulian_et_al:LIPIcs.IPEC.2015.236, author = {Bulian, Jannis and Dawar, Anuj}, title = {{Fixed-parameter Tractable Distances to Sparse Graph Classes}}, booktitle = {10th International Symposium on Parameterized and Exact Computation (IPEC 2015)}, pages = {236--247}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-92-7}, ISSN = {1868-8969}, year = {2015}, volume = {43}, editor = {Husfeldt, Thore and Kanj, Iyad}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.IPEC.2015.236}, URN = {urn:nbn:de:0030-drops-55865}, doi = {10.4230/LIPIcs.IPEC.2015.236}, annote = {Keywords: parameterized complexity, fixed-parameter tractable, distance, graph theory, sparse graphs, graph minor, nowhere dense} }

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**Published in:** LIPIcs, Volume 41, 24th EACSL Annual Conference on Computer Science Logic (CSL 2015)

The eleventh Ackermann Award is presented at CSL'15 in Berlin, Germany. This year, again, the EACSL Ackermann Award is generously sponsored by the Kurt Gödel Society. Besides providing financial support for the Ackermann Award, the Kurt Gödel Society has also committed to inviting the recipients of the Award for a special lecture to be given to the Society in Vienna.

Anuj Dawar, Dexter Kozen, and Simona Ronchi Della Rocca. The Ackermann Award 2015. In 24th EACSL Annual Conference on Computer Science Logic (CSL 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 41, pp. 15-18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{dawar_et_al:LIPIcs.CSL.2015.xv, author = {Dawar, Anuj and Kozen, Dexter and Ronchi Della Rocca, Simona}, title = {{The Ackermann Award 2015}}, booktitle = {24th EACSL Annual Conference on Computer Science Logic (CSL 2015)}, pages = {15--18}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-90-3}, ISSN = {1868-8969}, year = {2015}, volume = {41}, editor = {Kreutzer, Stephan}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2015.xv}, URN = {urn:nbn:de:0030-drops-54470}, doi = {10.4230/LIPIcs.CSL.2015.xv}, annote = {Keywords: Ackermann Award} }

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**Published in:** LIPIcs, Volume 41, 24th EACSL Annual Conference on Computer Science Logic (CSL 2015)

Finite valued constraint satisfaction problems are a formalism for describing many natural optimisation problems, where constraints on the values that variables can take come with rational weights and the aim is to find an assignment of minimal cost. Thapper and Zivny have recently established a complexity dichotomy for valued constraint languages. They show that each such languages either gives rise to a polynomial-time solvable optimisation problem, or to an NP-hard one, and establish a criterion to distinguish the two cases. We refine the dichotomy by showing that all optimisation problems in the first class are definable in fixed-point language with counting, while all languages in the second class are not definable, even in infinitary logic with counting. Our definability dichotomy is not conditional on any complexity-theoretic assumption.

Anuj Dawar and Pengming Wang. A Definability Dichotomy for Finite Valued CSPs. In 24th EACSL Annual Conference on Computer Science Logic (CSL 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 41, pp. 60-77, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{dawar_et_al:LIPIcs.CSL.2015.60, author = {Dawar, Anuj and Wang, Pengming}, title = {{A Definability Dichotomy for Finite Valued CSPs}}, booktitle = {24th EACSL Annual Conference on Computer Science Logic (CSL 2015)}, pages = {60--77}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-90-3}, ISSN = {1868-8969}, year = {2015}, volume = {41}, editor = {Kreutzer, Stephan}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2015.60}, URN = {urn:nbn:de:0030-drops-54078}, doi = {10.4230/LIPIcs.CSL.2015.60}, annote = {Keywords: descriptive complexity, constraint satisfaction, definability, fixed-point logic, optimization} }

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**Published in:** LIPIcs, Volume 25, 31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014)

We study properties of relational structures such as graphs that are decided by families of Boolean circuits. Circuits that decide such properties are necessarily invariant to permutations of the elements of the input structures. We focus on families of circuits that are symmetric, i.e., circuits whose invariance is witnessed by automorphisms of the circuit induced by the permutation of the input structure. We show that the expressive power of such families is closely tied to definability in logic. In particular, we show that the queries defined on structures by uniform families of symmetric Boolean circuits with majority gates are exactly those definable in fixed-point logic with counting. This shows that inexpressibility results in the latter logic lead to lower bounds against polynomial-size families of symmetric circuits.

Matthew Anderson and Anuj Dawar. On Symmetric Circuits and Fixed-Point Logics. In 31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014). Leibniz International Proceedings in Informatics (LIPIcs), Volume 25, pp. 41-52, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2014)

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@InProceedings{anderson_et_al:LIPIcs.STACS.2014.41, author = {Anderson, Matthew and Dawar, Anuj}, title = {{On Symmetric Circuits and Fixed-Point Logics}}, booktitle = {31st International Symposium on Theoretical Aspects of Computer Science (STACS 2014)}, pages = {41--52}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-65-1}, ISSN = {1868-8969}, year = {2014}, volume = {25}, editor = {Mayr, Ernst W. and Portier, Natacha}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2014.41}, URN = {urn:nbn:de:0030-drops-44455}, doi = {10.4230/LIPIcs.STACS.2014.41}, annote = {Keywords: symmetric circuit, fixed-point logic, majority, counting, uniformity} }

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**Published in:** LIPIcs, Volume 23, Computer Science Logic 2013 (CSL 2013)

Report on the Ackermann Award 2013.

Anuj Dawar, Thomas A. Henzinger, and Damian Niwiński. The Ackermann Award 2013. In Computer Science Logic 2013 (CSL 2013). Leibniz International Proceedings in Informatics (LIPIcs), Volume 23, pp. 1-4, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2013)

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@InProceedings{dawar_et_al:LIPIcs.CSL.2013.1, author = {Dawar, Anuj and Henzinger, Thomas A. and Niwi\'{n}ski, Damian}, title = {{The Ackermann Award 2013}}, booktitle = {Computer Science Logic 2013 (CSL 2013)}, pages = {1--4}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-60-6}, ISSN = {1868-8969}, year = {2013}, volume = {23}, editor = {Ronchi Della Rocca, Simona}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2013.1}, URN = {urn:nbn:de:0030-drops-41837}, doi = {10.4230/LIPIcs.CSL.2013.1}, annote = {Keywords: Ackermann award} }

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**Published in:** LIPIcs, Volume 16, Computer Science Logic (CSL'12) - 26th International Workshop/21st Annual Conference of the EACSL (2012)

Report on the Ackermann Award 2012.

Thierry Coquand, Anuj Dawar, and Damian Niwinski. The Ackermann Award 2012. In Computer Science Logic (CSL'12) - 26th International Workshop/21st Annual Conference of the EACSL. Leibniz International Proceedings in Informatics (LIPIcs), Volume 16, pp. 1-5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2012)

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@InProceedings{coquand_et_al:LIPIcs.CSL.2012.1, author = {Coquand, Thierry and Dawar, Anuj and Niwinski, Damian}, title = {{The Ackermann Award 2012}}, booktitle = {Computer Science Logic (CSL'12) - 26th International Workshop/21st Annual Conference of the EACSL}, pages = {1--5}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-42-2}, ISSN = {1868-8969}, year = {2012}, volume = {16}, editor = {C\'{e}gielski, Patrick and Durand, Arnaud}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2012.1}, URN = {urn:nbn:de:0030-drops-36575}, doi = {10.4230/LIPIcs.CSL.2012.1}, annote = {Keywords: Ackermann Award 2012} }

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**Published in:** LIPIcs, Volume 16, Computer Science Logic (CSL'12) - 26th International Workshop/21st Annual Conference of the EACSL (2012)

Motivated by the quest for a logic for PTIME and recent insights that the descriptive complexity of problems from linear algebra is a crucial aspect of this problem, we study the solvability of linear equation systems over finite groups and rings from the viewpoint of logical (inter-)definability. All problems that we consider are decidable in polynomial time, but not expressible in fixed-point logic with counting. They also provide natural candidates for a separation of polynomial time from rank logics, which extend fixed-point logics by operators for determining the rank of definable matrices and which are sufficient for solvability problems over fields.
Based on the structure theory of finite rings, we establish logical reductions among various solvability problems. Our results indicate that all solvability problems for linear equation systems that separate fixed-point logic with counting from PTIME can be reduced to solvability over commutative rings. Further, we prove closure properties for classes of queries that reduce to solvability over rings. As an application, these closure properties provide normal forms for logics extended with solvability operators.

Anuj Dawar, Erich Grädel, Bjarki Holm, Eryk Kopczynski, and Wied Pakusa. Definability of linear equation systems over groups and rings. In Computer Science Logic (CSL'12) - 26th International Workshop/21st Annual Conference of the EACSL. Leibniz International Proceedings in Informatics (LIPIcs), Volume 16, pp. 213-227, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2012)

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@InProceedings{dawar_et_al:LIPIcs.CSL.2012.213, author = {Dawar, Anuj and Gr\"{a}del, Erich and Holm, Bjarki and Kopczynski, Eryk and Pakusa, Wied}, title = {{Definability of linear equation systems over groups and rings}}, booktitle = {Computer Science Logic (CSL'12) - 26th International Workshop/21st Annual Conference of the EACSL}, pages = {213--227}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-42-2}, ISSN = {1868-8969}, year = {2012}, volume = {16}, editor = {C\'{e}gielski, Patrick and Durand, Arnaud}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2012.213}, URN = {urn:nbn:de:0030-drops-36749}, doi = {10.4230/LIPIcs.CSL.2012.213}, annote = {Keywords: inite model theory, logics with algebraic operators} }

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**Published in:** LIPIcs, Volume 4, IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (2009)

We investigate the parameterized complexity of generalisations and variations
of the dominating set problem on classes of graphs that are nowhere dense. In
particular, we show that the distance-$d$ dominating-set problem, also known
as the $(k,d)$-centres problem, is fixed-parameter tractable on any class that
is nowhere dense and closed under induced subgraphs. This generalises known
results about the dominating set problem on $H$-minor free classes, classes
with locally excluded minors and classes of graphs of bounded expansion. A
key feature of our proof is that it is based simply on the fact that these
graph classes are uniformly quasi-wide, and does not rely on a structural
decomposition. Our result also establishes that the distance-$d$
dominating-set problem is FPT on classes of bounded expansion, answering a
question of Ne{\v s}et{\v r}il and Ossona de Mendez.

Anuj Dawar and Stephan Kreutzer. Domination Problems in Nowhere-Dense Classes. In IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science. Leibniz International Proceedings in Informatics (LIPIcs), Volume 4, pp. 157-168, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2009)

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@InProceedings{dawar_et_al:LIPIcs.FSTTCS.2009.2315, author = {Dawar, Anuj and Kreutzer, Stephan}, title = {{Domination Problems in Nowhere-Dense Classes}}, booktitle = {IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science}, pages = {157--168}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-13-2}, ISSN = {1868-8969}, year = {2009}, volume = {4}, editor = {Kannan, Ravi and Narayan Kumar, K.}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2009.2315}, URN = {urn:nbn:de:0030-drops-23153}, doi = {10.4230/LIPIcs.FSTTCS.2009.2315}, annote = {Keywords: Dominating Set, distance-d dominating set, nowhere-dense graph classes, H-minor free graphs, fixed-parameter tractablility} }

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**Published in:** LIPIcs, Volume 4, IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (2009)

If computational complexity is the study of what makes certain computational
problems inherently difficult to solve, an important contribution of
descriptive complexity in this regard is the separation it provides between
the specification of a decision problem and the structure against which this
specification is checked. The formalisation of these two aspects leads to
tools for studying them as sources of complexity, and on the one hand leads to
results in the characterisation of complexity classes and on the other elates
to parameterized complexity. In these notes accompanying the invited talk,
some definitions and results are presented leading to recent work on the
characterisation of polynomial time and on the parameterized complexity of
first-order logic on restricted graph classes.

Anuj Dawar. Structure and Specification as Sources of Complexity. In IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science. Leibniz International Proceedings in Informatics (LIPIcs), Volume 4, pp. 407-416, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2009)

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@InProceedings{dawar:LIPIcs.FSTTCS.2009.2336, author = {Dawar, Anuj}, title = {{Structure and Specification as Sources of Complexity}}, booktitle = {IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science}, pages = {407--416}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-13-2}, ISSN = {1868-8969}, year = {2009}, volume = {4}, editor = {Kannan, Ravi and Narayan Kumar, K.}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2009.2336}, URN = {urn:nbn:de:0030-drops-23365}, doi = {10.4230/LIPIcs.FSTTCS.2009.2336}, annote = {Keywords: Computational Complexity, Descriptive Complexity, Logical Complexity, Parametrized Complexity, Locality, Automata} }