7 Search Results for "Ishihara, Hajime"

Document
DOI: 10.4230/LIPIcs.CSL.2026.24
Well-Founded Coalgebras Meet Kőnig’s Lemma

Authors: Henning Urbat and Thorsten Wißmann

Published in: LIPIcs, Volume 363, 34th EACSL Annual Conference on Computer Science Logic (CSL 2026)

Abstract
Kőnig’s lemma is a fundamental result about trees with countless applications in mathematics and computer science. In contrapositive form, it states that if a tree is finitely branching and well-founded (i.e. has no infinite paths), then it is finite. We present a coalgebraic version of Kőnig’s lemma featuring two dimensions of generalization: from finitely branching trees to coalgebras for a finitary endofunctor H, and from the base category of sets to a locally finitely presentable category ℂ, such as the category of posets, nominal sets, or convex sets. Our coalgebraic Kőnig’s lemma states that, under mild assumptions on ℂ and H, every well-founded coalgebra for H is the directed join of its well-founded subcoalgebras with finitely generated state space - in particular, the category of well-founded coalgebras is locally presentable. As applications, we derive versions of Kőnig’s lemma for graphs in a topos as well as for nominal and convex transition systems. Additionally, we show that the key construction underlying the proof gives rise to two simple constructions of the initial algebra (equivalently, the final recursive coalgebra) for the functor H: The initial algebra is both the colimit of all well-founded and of all recursive coalgebras with finitely presentable state space. Remarkably, this result holds even in settings where well-founded coalgebras form a proper subclass of recursive ones. The first construction of the initial algebra is entirely new, while for the second one our approach yields a short and transparent new correctness proof.
Cite as

Henning Urbat and Thorsten Wißmann. Well-Founded Coalgebras Meet Kőnig’s Lemma. In 34th EACSL Annual Conference on Computer Science Logic (CSL 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 363, pp. 24:1-24:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{urbat_et_al:LIPIcs.CSL.2026.24,
  author =	{Urbat, Henning and Wi{\ss}mann, Thorsten},
  title =	{{Well-Founded Coalgebras Meet K\H{o}nig’s Lemma}},
  booktitle =	{34th EACSL Annual Conference on Computer Science Logic (CSL 2026)},
  pages =	{24:1--24:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-411-6},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{363},
  editor =	{Guerrini, Stefano and K\"{o}nig, Barbara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2026.24},
  URN =		{urn:nbn:de:0030-drops-254485},
  doi =		{10.4230/LIPIcs.CSL.2026.24},
  annote =	{Keywords: K\H{o}nig’s Lemma, Well-Foundedness, Coalgebra}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2025.66
Deciding Regular Games: a Playground for Exponential Time Algorithms

Authors: Zihui Liang, Bakh Khoussainov, and Mingyu Xiao

Published in: LIPIcs, Volume 345, 50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025)

Abstract
Regular games form a well-established class of games for analysis and synthesis of reactive systems. They include colored Muller games, McNaughton games, Muller games, Rabin games, and Streett games. These games are played on directed graphs G where Player 0 and Player 1 play by generating an infinite path ρ through the graph. The winner is determined by specifications put on the set X of vertices in ρ that occur infinitely often. These games are determined, enabling the partitioning of G into two sets Win₀ and Win₁ of winning positions for Player 0 and Player 1, respectively. Numerous algorithms exist that decide instances of regular games, e.g., Muller games, by computing Win₀ and Win₁. In this paper we aim to find general principles for designing uniform algorithms that decide all regular games. For this we utilize various recursive and dynamic programming algorithms that leverage standard notions such as subgames and traps. Importantly, we show that our techniques improve or match the performances of existing algorithms for many instances of regular games.
Cite as

Zihui Liang, Bakh Khoussainov, and Mingyu Xiao. Deciding Regular Games: a Playground for Exponential Time Algorithms. In 50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 345, pp. 66:1-66:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{liang_et_al:LIPIcs.MFCS.2025.66,
  author =	{Liang, Zihui and Khoussainov, Bakh and Xiao, Mingyu},
  title =	{{Deciding Regular Games: a Playground for Exponential Time Algorithms}},
  booktitle =	{50th International Symposium on Mathematical Foundations of Computer Science (MFCS 2025)},
  pages =	{66:1--66:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-388-1},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{345},
  editor =	{Gawrychowski, Pawe{\l} and Mazowiecki, Filip and Skrzypczak, Micha{\l}},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2025.66},
  URN =		{urn:nbn:de:0030-drops-241732},
  doi =		{10.4230/LIPIcs.MFCS.2025.66},
  annote =	{Keywords: Regular games, colored Muller games, Rabin games, McNaughton games, Muller games, deciding games}
}
Document
DOI: 10.4230/LIPIcs.TYPES.2024.3
A Foundation for Synthetic Stone Duality

Authors: Felix Cherubini, Thierry Coquand, Freek Geerligs, and Hugo Moeneclaey

Published in: LIPIcs, Volume 336, 30th International Conference on Types for Proofs and Programs (TYPES 2024)

Abstract
The language of homotopy type theory has proved to be an appropriate internal language for various higher toposes, for example for the Zariski topos in Synthetic Algebraic Geometry. This paper aims to do the same for the higher topos of light condensed anima of Dustin Clausen and Peter Scholze. This seems to be an appropriate setting for synthetic topology in the style of Martín Escardó. We use homotopy type theory extended with 4 axioms. We prove Markov’s principle, LLPO and the negation of WLPO. Then we define a type of open propositions, inducing a topology on any type such that any map is continuous. We give a synthetic definition of second countable Stone and compact Hausdorff spaces, and show that their induced topologies are as expected. This means that any map from e.g. the unit interval 𝕀 to itself is continuous in the usual epsilon-delta sense. With the usual definition of cohomology in homotopy type theory, we show that H¹(S,ℤ) = 0 for S Stone and that H¹(X,ℤ) for X compact Hausdorff can be computed using Čech cohomology. We use this to prove H¹(𝕀¹,ℤ) = 0 and H¹(𝕊¹,ℤ) = ℤ where 𝕊¹ is the set ℝ/ℤ. As an application, we give a synthetic proof of Brouwer’s fixed-point theorem.
Cite as

Felix Cherubini, Thierry Coquand, Freek Geerligs, and Hugo Moeneclaey. A Foundation for Synthetic Stone Duality. In 30th International Conference on Types for Proofs and Programs (TYPES 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 336, pp. 3:1-3:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{cherubini_et_al:LIPIcs.TYPES.2024.3,
  author =	{Cherubini, Felix and Coquand, Thierry and Geerligs, Freek and Moeneclaey, Hugo},
  title =	{{A Foundation for Synthetic Stone Duality}},
  booktitle =	{30th International Conference on Types for Proofs and Programs (TYPES 2024)},
  pages =	{3:1--3:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-376-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{336},
  editor =	{M{\o}gelberg, Rasmus Ejlers and van den Berg, Benno},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2024.3},
  URN =		{urn:nbn:de:0030-drops-233659},
  doi =		{10.4230/LIPIcs.TYPES.2024.3},
  annote =	{Keywords: Homotopy Type Theory, Synthetic Topology, Cohomology}
}
Document
DOI: 10.4230/DagRep.14.1.1
From Proofs to Computation in Geometric Logic and Generalizations (Dagstuhl Seminar 24021)

Authors: Ingo Blechschmidt, Hajime Ishihara, Peter M. Schuster, and Gabriele Buriola

Published in: Dagstuhl Reports, Volume 14, Issue 1 (2024)

Abstract
What is the computational content of proofs? This is one of the main topics in mathematical logic, especially proof theory, that is of relevance for computer science. The well-known foundational solutions aim at rebuilding mathematics constructively almost from scratch, and include Bishop-style constructive mathematics and Martin-Löf’s intuitionistic type theory, the latter most recently in the form of the so-called homotopy or univalent type theory put forward by Voevodsky. From a more practical angle, however, the question rather is to which extent any given proof is effective, which proofs of which theorems can be rendered effective, and whether and how numerical information such as bounds and algorithms can be extracted from proofs. Ideally, all this is done by manipulating proofs mechanically and/or by adequate metatheorems (proof translations, automated theorem proving, program extraction from proofs, proof mining, etc.). A crucial role for answering these questions is played by coherent and geometric theories and their generalizations: not only that they are fairly widespread in modern mathematics and non-classical logics (e.g., in abstract algebra, and in temporal and modal logics); those theories are also a priori amenable for constructivisation (see Barr’s Theorem, especially its proof-theoretic variants, and the numerous Glivenko–style theorems); last but not least, effective theorem-proving for coherent theories can be automated with relative ease and clarity in relation to resolution. Specific topics that substantially involve computer science research include categorical semantics for geometric theories up to the proof-theoretic presentation of sheaf models and higher toposes; extracting the computational content of proofs and dynamical methods in quadratic form theory; the interpretation of transfinite proof methods as latent computations; complexity issues of and algorithms for geometrization of theories; the use of geometric theories in constructive mathematics including finding algorithms, ideally with integrated developments; and coherent logic for obtaining automatically readable proofs.
Cite as

Ingo Blechschmidt, Hajime Ishihara, Peter M. Schuster, and Gabriele Buriola. From Proofs to Computation in Geometric Logic and Generalizations (Dagstuhl Seminar 24021). In Dagstuhl Reports, Volume 14, Issue 1, pp. 1-24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@Article{blechschmidt_et_al:DagRep.14.1.1,
  author =	{Blechschmidt, Ingo and Ishihara, Hajime and Schuster, Peter M. and Buriola, Gabriele},
  title =	{{From Proofs to Computation in Geometric Logic and Generalizations (Dagstuhl Seminar 24021)}},
  pages =	{1--24},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2024},
  volume =	{14},
  number =	{1},
  editor =	{Blechschmidt, Ingo and Ishihara, Hajime and Schuster, Peter M. and Buriola, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.14.1.1},
  URN =		{urn:nbn:de:0030-drops-204882},
  doi =		{10.4230/DagRep.14.1.1},
  annote =	{Keywords: automated theorem proving, categorical semantics, constructivisation, geometric logic, proof theory}
}
Document
DOI: 10.4230/DagRep.11.10.151
Geometric Logic, Constructivisation, and Automated Theorem Proving (Dagstuhl Seminar 21472)

Authors: Thierry Coquand, Hajime Ishihara, Sara Negri, and Peter M. Schuster

Published in: Dagstuhl Reports, Volume 11, Issue 10 (2022)

Abstract
At least from a practical and contemporary angle, the time-honoured question about the extent of intuitionistic mathematics rather is to which extent any given proof is effective, which proofs of which theorems can be rendered effective, and whether and how numerical information such as bounds and algorithms can be extracted from proofs. All this is ideally done by manipulating proofs mechanically or by adequate metatheorems, which includes proof translations, automated theorem proving, program extraction from proofs, proof analysis and proof mining. The question should thus be put as: What is the computational content of proofs? Guided by this central question, the present Dagstuhl seminar puts a special focus on coherent and geometric theories and their generalisations. These are not only widespread in mathematics and non-classical logics such as temporal and modal logics, but also a priori amenable for constructivisation, e.g., by Barr’s Theorem, and last but not least particularly suited as a basis for automated theorem proving. Specific topics include categorical semantics for geometric theories, complexity issues of and algorithms for geometrisation of theories including speed-up questions, the use of geometric theories in constructive mathematics including finding algorithms, proof-theoretic presentation of sheaf models and higher toposes, and coherent logic for automatically readable proofs.
Cite as

Thierry Coquand, Hajime Ishihara, Sara Negri, and Peter M. Schuster. Geometric Logic, Constructivisation, and Automated Theorem Proving (Dagstuhl Seminar 21472). In Dagstuhl Reports, Volume 11, Issue 10, pp. 151-172, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@Article{coquand_et_al:DagRep.11.10.151,
  author =	{Coquand, Thierry and Ishihara, Hajime and Negri, Sara and Schuster, Peter M.},
  title =	{{Geometric Logic, Constructivisation, and Automated Theorem Proving (Dagstuhl Seminar 21472)}},
  pages =	{151--172},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2022},
  volume =	{11},
  number =	{10},
  editor =	{Coquand, Thierry and Ishihara, Hajime and Negri, Sara and Schuster, Peter M.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.11.10.151},
  URN =		{urn:nbn:de:0030-drops-159321},
  doi =		{10.4230/DagRep.11.10.151},
  annote =	{Keywords: automated theorem proving, categorical semantics, constructivisation, geometric logic, proof theory}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2020.25
A Gentzen-Style Monadic Translation of Gödel’s System T

Authors: Chuangjie Xu

Published in: LIPIcs, Volume 167, 5th International Conference on Formal Structures for Computation and Deduction (FSCD 2020)

Abstract
We introduce a syntactic translation of Gödel’s System 𝖳 parametrized by a weak notion of a monad, and prove a corresponding fundamental theorem of logical relation. Our translation structurally corresponds to Gentzen’s negative translation of classical logic. By instantiating the monad and the logical relation, we reveal the well-known properties and structures of 𝖳-definable functionals including majorizability, continuity and bar recursion. Our development has been formalized in the Agda proof assistant.
Cite as

Chuangjie Xu. A Gentzen-Style Monadic Translation of Gödel’s System T. In 5th International Conference on Formal Structures for Computation and Deduction (FSCD 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 167, pp. 25:1-25:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{xu:LIPIcs.FSCD.2020.25,
  author =	{Xu, Chuangjie},
  title =	{{A Gentzen-Style Monadic Translation of G\"{o}del’s System T}},
  booktitle =	{5th International Conference on Formal Structures for Computation and Deduction (FSCD 2020)},
  pages =	{25:1--25:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-155-9},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{167},
  editor =	{Ariola, Zena M.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2020.25},
  URN =		{urn:nbn:de:0030-drops-123472},
  doi =		{10.4230/LIPIcs.FSCD.2020.25},
  annote =	{Keywords: monadic translation, G\"{o}del’s System T, logical relation, negative translation, majorizability, continuity, bar recursion, Agda}
}
Document
DOI: 10.4230/DagSemProc.04351.9
Compactness in apartness spaces?

Authors: Douglas Bridges, Hajime Ishihara, Peter Schuster, and Luminita S. Vita

Published in: Dagstuhl Seminar Proceedings, Volume 4351, Spatial Representation: Discrete vs. Continuous Computational Models (2005)

Abstract
A major problem in the constructive theory of apartness spaces is that of finding a good notion of compactness. Such a notion should (i) reduce to ``complete plus totally bounded'' for uniform spaces and (ii) classically be equivalent to the usual Heine-Borel-Lebesgue property for the apartness topology. The constructive counterpart of the smallest uniform structure compatible with a given apartness, while not constructively a uniform structure, offers a possible solution to the compactness-definition problem. That counterpart turns out to be interesting in its own right, and reveals some additional properties of an apartness that may have uses elsewhere in the theory.
Cite as

Douglas Bridges, Hajime Ishihara, Peter Schuster, and Luminita S. Vita. Compactness in apartness spaces?. In Spatial Representation: Discrete vs. Continuous Computational Models. Dagstuhl Seminar Proceedings, Volume 4351, pp. 1-7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2005)

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@InProceedings{bridges_et_al:DagSemProc.04351.9,
  author =	{Bridges, Douglas and Ishihara, Hajime and Schuster, Peter and Vita, Luminita S.},
  title =	{{Compactness in apartness spaces?}},
  booktitle =	{Spatial Representation: Discrete vs. Continuous Computational Models},
  pages =	{1--7},
  series =	{Dagstuhl Seminar Proceedings (DagSemProc)},
  ISSN =	{1862-4405},
  year =	{2005},
  volume =	{4351},
  editor =	{Ralph Kopperman and Michael B. Smyth and Dieter Spreen and Julian Webster},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.04351.9},
  URN =		{urn:nbn:de:0030-drops-1175},
  doi =		{10.4230/DagSemProc.04351.9},
  annote =	{Keywords: Apartness , constructive , compact uniform space}
}
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