6 Search Results for "Hetzl, Stefan"

Document
DOI: 10.4230/LIPIcs.FSCD.2025.32
Interpolation as Cut-Introduction: On the Computational Content of Craig-Lyndon Interpolation

Authors: Alexis Saurin

Published in: LIPIcs, Volume 337, 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)

Abstract
Analyzing Maehara’s method for proving Craig’s interpolation theorem, we extract a "proof relevant" interpolation theorem for first-order LL in the sense that if π is a cut-free sequent proof of A⊢ B, we can find a formula C in the common vocabulary of A and B and proofs π₁,π₂ of A⊢ C and C⊢ B respectively such that π₁ composed with π₂ cut-reduces to π. As a direct corollary, we get similar proof relevant interpolation results for LJ and LK using linear translations. This refined interpolation is then rephrased in terms of a cut-introduction process synthetizing the interpolant. Finally, we analyze the computational content of interpolation by proving an interpolation result for Curien and Herbelin’s Duality of Computation.
Cite as

Alexis Saurin. Interpolation as Cut-Introduction: On the Computational Content of Craig-Lyndon Interpolation. In 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 337, pp. 32:1-32:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{saurin:LIPIcs.FSCD.2025.32,
  author =	{Saurin, Alexis},
  title =	{{Interpolation as Cut-Introduction: On the Computational Content of Craig-Lyndon Interpolation}},
  booktitle =	{10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)},
  pages =	{32:1--32:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-374-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{337},
  editor =	{Fern\'{a}ndez, Maribel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2025.32},
  URN =		{urn:nbn:de:0030-drops-236478},
  doi =		{10.4230/LIPIcs.FSCD.2025.32},
  annote =	{Keywords: Classical Logic, Interpolation, Cut Elimination, Linear Logic, Sequent calculus, System L}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2025.29
Linear Logic Using Negative Connectives

Authors: Dale Miller

Published in: LIPIcs, Volume 337, 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)

Abstract
In linear logic, the invertibility of a connective’s right-introduction rule is equivalent to the non-invertibility of its left-introduction rule. This duality motivates the concept of polarity: a connective is termed negative if its right-introduction rule is invertible, and positive otherwise. A two-sided sequent calculus for first-order linear logic featuring only negative connectives exhibits a compelling proof theory. Proof search in such a system unfolds through alternating phases of invertible (right-introduction) rules and non-invertible (left-introduction) rules, mirroring the processes of goal-reduction and backchaining, respectively. These phases are formalized here using the framework of multifocused proofs. We analyze linear logic by dissecting it into three sublogics: L₀ (first-order intuitionistic logic with conjunction, implication, and universal quantification); L₁ (an extension of L₀ incorporating linear implication which preserves its intuitionistic nature); and L₂ (which includes multiplicative falsity ⊥ and encompasses classical linear logic). It is worth noting that the single-conclusion restriction on sequents, a constraint imposed by Gentzen, is not a prerequisite for defining intuitionistic logic proofs within this framework, as it emerges naturally by restricting the formulas to those of L₀ and L₁. While multifocused proofs of L₂ sequents can accommodate parallel applications of left-introduction rules, proofs of L₀ and L₁ sequents cannot leverage such parallel rule applications. This notion of parallelism within proofs enables a novel approach to handling disjunctions and existential quantifiers in the natural deduction system for intuitionistic logic.
Cite as

Dale Miller. Linear Logic Using Negative Connectives. In 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 337, pp. 29:1-29:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{miller:LIPIcs.FSCD.2025.29,
  author =	{Miller, Dale},
  title =	{{Linear Logic Using Negative Connectives}},
  booktitle =	{10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)},
  pages =	{29:1--29:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-374-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{337},
  editor =	{Fern\'{a}ndez, Maribel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2025.29},
  URN =		{urn:nbn:de:0030-drops-236442},
  doi =		{10.4230/LIPIcs.FSCD.2025.29},
  annote =	{Keywords: Linear logic, multifocused proofs, sequent calculus}
}
Document
DOI: 10.4230/LIPIcs.CSL.2015.110
Tree Grammars for the Elimination of Non-prenex Cuts

Authors: Stefan Hetzl and Sebastian Zivota

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

Abstract
Recently a new connection between proof theory and formal language theory was introduced. It was shown that the operation of cut elimination for proofs with prenex Pi_1-cuts in classical first-order logic corresponds to computing the language of a particular type of tree grammars. The present paper extends this connection to arbitrary (i.e. non-prenex) cuts without quantifier alternations. The key to treating non-prenex cuts lies in using a new class of tree grammars, constraint grammars, which describe the relationship of the applicability of its productions by a propositional formula.
Cite as

Stefan Hetzl and Sebastian Zivota. Tree Grammars for the Elimination of Non-prenex Cuts. In 24th EACSL Annual Conference on Computer Science Logic (CSL 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 41, pp. 110-127, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{hetzl_et_al:LIPIcs.CSL.2015.110,
  author =	{Hetzl, Stefan and Zivota, Sebastian},
  title =	{{Tree Grammars for the Elimination of Non-prenex Cuts}},
  booktitle =	{24th EACSL Annual Conference on Computer Science Logic (CSL 2015)},
  pages =	{110--127},
  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.2015.110},
  URN =		{urn:nbn:de:0030-drops-54103},
  doi =		{10.4230/LIPIcs.CSL.2015.110},
  annote =	{Keywords: proof theory, cut-elimination, Herbrand's theorem, tree grammars}
}
Document
DOI: 10.4230/LIPIcs.TLCA.2015.1
Herbrand Disjunctions, Cut Elimination and Context-Free Tree Grammars

Authors: Bahareh Afshari, Stefan Hetzl, and Graham E. Leigh

Published in: LIPIcs, Volume 38, 13th International Conference on Typed Lambda Calculi and Applications (TLCA 2015)

Abstract
Recently a new connection between proof theory and formal language theory was introduced. It was shown that the operation of cut elimination for proofs in first-order predicate logic involving Pi_1-cuts corresponds to computing the language of a particular class of regular tree grammars. The present paper expands this connection to the level of Pi_2-cuts. Given a proof pi of a Sigma_1 formula with cuts only on Pi_2 formulæ, we show there is associated to pi a natural context-free tree grammar whose language is finite and yields a Herbrand disjunction for pi.
Cite as

Bahareh Afshari, Stefan Hetzl, and Graham E. Leigh. Herbrand Disjunctions, Cut Elimination and Context-Free Tree Grammars. In 13th International Conference on Typed Lambda Calculi and Applications (TLCA 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 38, pp. 1-16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{afshari_et_al:LIPIcs.TLCA.2015.1,
  author =	{Afshari, Bahareh and Hetzl, Stefan and Leigh, Graham E.},
  title =	{{Herbrand Disjunctions, Cut Elimination and Context-Free Tree Grammars}},
  booktitle =	{13th International Conference on Typed Lambda Calculi and Applications (TLCA 2015)},
  pages =	{1--16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-87-3},
  ISSN =	{1868-8969},
  year =	{2015},
  volume =	{38},
  editor =	{Altenkirch, Thorsten},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TLCA.2015.1},
  URN =		{urn:nbn:de:0030-drops-51516},
  doi =		{10.4230/LIPIcs.TLCA.2015.1},
  annote =	{Keywords: Classical logic, Context-free grammars, Cut elimination, First-order logic, Herbrand's theorem, Proof theory}
}
Document
DOI: 10.4230/LIPIcs.CSL.2012.183
A Systematic Approach to Canonicity in the Classical Sequent Calculus

Authors: Kaustuv Chaudhuri, Stefan Hetzl, and Dale Miller

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

Abstract
The sequent calculus is often criticized for requiring proofs to contain large amounts of low-level syntactic details that can obscure the essence of a given proof. Because each inference rule introduces only a single connective, sequent proofs can separate closely related steps-such as instantiating a block of quantifiers-by irrelevant noise. Moreover, the sequential nature of sequent proofs forces proof steps that are syntactically non-interfering and permutable to nevertheless be written in some arbitrary order. The sequent calculus thus lacks a notion of canonicity: proofs that should be considered essentially the same may not have a common syntactic form. To fix this problem, many researchers have proposed replacing the sequent calculus with proof structures that are more parallel or geometric. Proof-nets, matings, and atomic flows are examples of such revolutionary formalisms. We propose, instead, an evolutionary approach to recover canonicity within the sequent calculus, which we illustrate for classical first-order logic. The essential element of our approach is the use of a multi-focused sequent calculus as the means of abstracting away the details from classical cut-free sequent proofs. We show that, among the multi-focused proofs, the maximally multi-focused proofs that make the foci as parallel as possible are canonical. Moreover, such proofs are isomorphic to expansion proofs - a well known, minimalistic, and parallel generalization of Herbrand disjunctions - for classical first-order logic. This technique is a systematic way to recover the desired essence of any sequent proof without abandoning the sequent calculus.
Cite as

Kaustuv Chaudhuri, Stefan Hetzl, and Dale Miller. A Systematic Approach to Canonicity in the Classical Sequent Calculus. In Computer Science Logic (CSL'12) - 26th International Workshop/21st Annual Conference of the EACSL. Leibniz International Proceedings in Informatics (LIPIcs), Volume 16, pp. 183-197, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2012)

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@InProceedings{chaudhuri_et_al:LIPIcs.CSL.2012.183,
  author =	{Chaudhuri, Kaustuv and Hetzl, Stefan and Miller, Dale},
  title =	{{A Systematic Approach to Canonicity in the Classical Sequent Calculus}},
  booktitle =	{Computer Science Logic (CSL'12) - 26th International Workshop/21st Annual Conference of the EACSL},
  pages =	{183--197},
  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.2012.183},
  URN =		{urn:nbn:de:0030-drops-36723},
  doi =		{10.4230/LIPIcs.CSL.2012.183},
  annote =	{Keywords: Sequent Calculus, Canonicity, Classical Logic, Expansion Trees}
}
Document
DOI: 10.4230/LIPIcs.CSL.2012.320
Herbrand-Confluence for Cut Elimination in Classical First Order Logic

Authors: Stefan Hetzl and Lutz Straßburger

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

Abstract
We consider cut-elimination in the sequent calculus for classical first-order logic. It is well known that this system, in its most general form, is neither confluent nor strongly normalizing. In this work we take a coarser (and mathematically more realistic) look at cut-free proofs. We analyze which witnesses they choose for which quantifiers, or in other words: we only consider the Herbrand-disjunction of a cut-free proof. Our main theorem is a confluence result for a natural class of proofs: all (possibly infinitely many) normal forms of the non-erasing reduction lead to the same Herbrand-disjunction.
Cite as

Stefan Hetzl and Lutz Straßburger. Herbrand-Confluence for Cut Elimination in Classical First Order Logic. In Computer Science Logic (CSL'12) - 26th International Workshop/21st Annual Conference of the EACSL. Leibniz International Proceedings in Informatics (LIPIcs), Volume 16, pp. 320-334, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2012)

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@InProceedings{hetzl_et_al:LIPIcs.CSL.2012.320,
  author =	{Hetzl, Stefan and Stra{\ss}burger, Lutz},
  title =	{{Herbrand-Confluence for Cut Elimination in Classical First Order Logic}},
  booktitle =	{Computer Science Logic (CSL'12) - 26th International Workshop/21st Annual Conference of the EACSL},
  pages =	{320--334},
  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.2012.320},
  URN =		{urn:nbn:de:0030-drops-36815},
  doi =		{10.4230/LIPIcs.CSL.2012.320},
  annote =	{Keywords: proof theory, first-order logic, tree languages, term rewriting, semantics of proofs}
}
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