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Documents authored by Spachmann, Luc Nicolas

Document
DOI: 10.4230/LIPIcs.SAT.2026.3
Proof Systems for QBF Synthesis: Extracting Skolem and Herbrand Functions

Authors: S. Akshay, Olaf Beyersdorff, Supratik Chakraborty, Lea Kasche, Meena Mahajan, and Luc Nicolas Spachmann

Published in: LIPIcs, Volume 377, 29th International Conference on Theory and Applications of Satisfiability Testing (SAT 2026)

Abstract
Strategy extraction in QBF proof systems usually attempts to extract winning strategies from valid proofs. However, an alternative (and arguably more powerful) view is to extract Skolem/Herbrand functions, or equivalently synthesis of the game values at all intermediate points. In this paper, we investigate the existence and properties of such proof systems from which one can extract Skolem and Herbrand functions. We propose such a proof system for QBF, which we show is sound and complete, and from which extraction of Skolem/Herbrand functions can be performed, and game values computed, in polynomial time. We also show that this system is optimal among all proof systems that allow efficient extraction of Skolem/Herbrand functions. We provide conditional lower bound results for our new proof system and compare it to several existing/standard proof systems for QBF that have been studied in the literature, showing interesting orthogonality results. Finally, we provide a compilation algorithm that takes an arbitrary QBF and synthesizes a proof in our system, from which Skolem and Herbrand functions can be easily computed.
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S. Akshay, Olaf Beyersdorff, Supratik Chakraborty, Lea Kasche, Meena Mahajan, and Luc Nicolas Spachmann. Proof Systems for QBF Synthesis: Extracting Skolem and Herbrand Functions. In 29th International Conference on Theory and Applications of Satisfiability Testing (SAT 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 377, pp. 3:1-3:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{akshay_et_al:LIPIcs.SAT.2026.3,
  author =	{Akshay, S. and Beyersdorff, Olaf and Chakraborty, Supratik and Kasche, Lea and Mahajan, Meena and Spachmann, Luc Nicolas},
  title =	{{Proof Systems for QBF Synthesis: Extracting Skolem and Herbrand Functions}},
  booktitle =	{29th International Conference on Theory and Applications of Satisfiability Testing (SAT 2026)},
  pages =	{3:1--3:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-431-4},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{377},
  editor =	{Ignatiev, Alexey and Szeider, Stefan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SAT.2026.3},
  URN =		{urn:nbn:de:0030-drops-263096},
  doi =		{10.4230/LIPIcs.SAT.2026.3},
  annote =	{Keywords: Quantified Boolean Formulas, Skolem and Herbrand functions, Automated synthesis, Knowledge compilation, Proof systems and complexity}
}
Document
DOI: 10.4230/LIPIcs.SAT.2025.5
Semi-Algebraic Proof Systems for QBF

Authors: Olaf Beyersdorff, Ilario Bonacina, Kaspar Kasche, Meena Mahajan, and Luc Nicolas Spachmann

Published in: LIPIcs, Volume 341, 28th International Conference on Theory and Applications of Satisfiability Testing (SAT 2025)

Abstract
We introduce new semi-algebraic proof systems for Quantified Boolean Formulas (QBF) analogous to the propositional systems Nullstellensatz, Sherali-Adams and Sum-of-Squares. We transfer to this setting techniques both from the QBF literature (strategy extraction) and from propositional proof complexity (size-degree relations and pseudo-expectation). We obtain a number of strong QBF lower bounds and separations between these systems, even when disregarding propositional hardness.
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Olaf Beyersdorff, Ilario Bonacina, Kaspar Kasche, Meena Mahajan, and Luc Nicolas Spachmann. Semi-Algebraic Proof Systems for QBF. In 28th International Conference on Theory and Applications of Satisfiability Testing (SAT 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 341, pp. 5:1-5:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{beyersdorff_et_al:LIPIcs.SAT.2025.5,
  author =	{Beyersdorff, Olaf and Bonacina, Ilario and Kasche, Kaspar and Mahajan, Meena and Spachmann, Luc Nicolas},
  title =	{{Semi-Algebraic Proof Systems for QBF}},
  booktitle =	{28th International Conference on Theory and Applications of Satisfiability Testing (SAT 2025)},
  pages =	{5:1--5:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-381-2},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{341},
  editor =	{Berg, Jeremias and Nordstr\"{o}m, Jakob},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SAT.2025.5},
  URN =		{urn:nbn:de:0030-drops-237394},
  doi =		{10.4230/LIPIcs.SAT.2025.5},
  annote =	{Keywords: QBF, Proof Complexity, Sums-of-Squares, Nullstellensatz, Sherali-Adams, Semi-Algebraic Proof Systems}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2024.27
Polynomial Calculus for Quantified Boolean Logic: Lower Bounds Through Circuits and Degree

Authors: Olaf Beyersdorff, Tim Hoffmann, Kaspar Kasche, and Luc Nicolas Spachmann

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

Abstract
We initiate an in-depth proof-complexity analysis of polynomial calculus (𝒬-PC) for Quantified Boolean Formulas (QBF). In the course of this we establish a tight proof-size characterisation of 𝒬-PC in terms of a suitable circuit model (polynomial decision lists). Using this correspondence we show a size-degree relation for 𝒬-PC, similar in spirit, yet different from the classic size-degree formula for propositional PC by Impagliazzo, Pudlák and Sgall (1999). We use the circuit characterisation together with the size-degree relation to obtain various new lower bounds on proof size in 𝒬-PC. This leads to incomparability results for 𝒬-PC systems over different fields.
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Olaf Beyersdorff, Tim Hoffmann, Kaspar Kasche, and Luc Nicolas Spachmann. Polynomial Calculus for Quantified Boolean Logic: Lower Bounds Through Circuits and Degree. In 49th International Symposium on Mathematical Foundations of Computer Science (MFCS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 306, pp. 27:1-27:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{beyersdorff_et_al:LIPIcs.MFCS.2024.27,
  author =	{Beyersdorff, Olaf and Hoffmann, Tim and Kasche, Kaspar and Spachmann, Luc Nicolas},
  title =	{{Polynomial Calculus for Quantified Boolean Logic: Lower Bounds Through Circuits and Degree}},
  booktitle =	{49th International Symposium on Mathematical Foundations of Computer Science (MFCS 2024)},
  pages =	{27:1--27:15},
  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.2024.27},
  URN =		{urn:nbn:de:0030-drops-205834},
  doi =		{10.4230/LIPIcs.MFCS.2024.27},
  annote =	{Keywords: proof complexity, QBF, polynomial calculus, circuits, lower bounds}
}
Document
DOI: 10.4230/LIPIcs.SAT.2023.2
Proof Complexity of Propositional Model Counting

Authors: Olaf Beyersdorff, Tim Hoffmann, and Luc Nicolas Spachmann

Published in: LIPIcs, Volume 271, 26th International Conference on Theory and Applications of Satisfiability Testing (SAT 2023)

Abstract
Recently, the proof system MICE for the model counting problem #SAT was introduced by Fichte, Hecher and Roland (SAT'22). As demonstrated by Fichte et al., the system MICE can be used for proof logging for state-of-the-art #SAT solvers. We perform a proof-complexity study of MICE. For this we first simplify the rules of MICE and obtain a calculus MICE' that is polynomially equivalent to MICE. Our main result establishes an exponential lower bound for the number of proof steps in MICE' (and hence also in MICE) for a specific family of CNFs.
Cite as

Olaf Beyersdorff, Tim Hoffmann, and Luc Nicolas Spachmann. Proof Complexity of Propositional Model Counting. In 26th International Conference on Theory and Applications of Satisfiability Testing (SAT 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 271, pp. 2:1-2:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{beyersdorff_et_al:LIPIcs.SAT.2023.2,
  author =	{Beyersdorff, Olaf and Hoffmann, Tim and Spachmann, Luc Nicolas},
  title =	{{Proof Complexity of Propositional Model Counting}},
  booktitle =	{26th International Conference on Theory and Applications of Satisfiability Testing (SAT 2023)},
  pages =	{2:1--2:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-286-0},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{271},
  editor =	{Mahajan, Meena and Slivovsky, Friedrich},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SAT.2023.2},
  URN =		{urn:nbn:de:0030-drops-184647},
  doi =		{10.4230/LIPIcs.SAT.2023.2},
  annote =	{Keywords: model counting, #SAT, proof complexity, proof systems, lower bounds}
}
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