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Documents authored by Cohen, Liron

Document
Invited Talk
DOI: 10.4230/LIPIcs.FSCD.2025.1
Computation First: Rebuilding Constructivism with Effects (Invited Talk)

Authors: Liron Cohen

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

Abstract
Constructive logic and type theory have traditionally been grounded in pure, effect-free model of computation. This paper argues that such a restriction is not a foundational necessity but a historical artifact, and it advocates for a broader perspective of effectful constructivism, where computational effects, such as state, non-determinism, and exceptions, are directly and internally embedded in the logical and computational foundations. We begin by surveying examples where effects reshape logical principles, and then outline three approaches to effectful constructivism, focusing on realizability models: Monadic Combinatory Algebras, which extend classical partial combinatory algebras with effectful computation; Evidenced Frames, a flexible semantic structure capable of uniformly capturing a wide range of effects; and Effectful Higher-Order Logic (EffHOL), a syntactic approach that directly translates logical propositions into specifications for effectful programs. We further illustrate how concrete type theories can internalize effects, via the family of type theories TT^□_C. Together, these works demonstrate that effectful constructivism is not merely possible but a natural and robust extension of traditional frameworks.
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Liron Cohen. Computation First: Rebuilding Constructivism with Effects (Invited Talk). In 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 337, pp. 1:1-1:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{cohen:LIPIcs.FSCD.2025.1,
  author =	{Cohen, Liron},
  title =	{{Computation First: Rebuilding Constructivism with Effects}},
  booktitle =	{10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)},
  pages =	{1:1--1:20},
  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.2025.1},
  URN =		{urn:nbn:de:0030-drops-236167},
  doi =		{10.4230/LIPIcs.FSCD.2025.1},
  annote =	{Keywords: Effectful constructivism, realizability, type theory, monadic combinatory algebras, evidenced frame}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2025.14
From Partial to Monadic: Combinatory Algebra with Effects

Authors: Liron Cohen, Ariel Grunfeld, Dominik Kirst, and Étienne Miquey

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

Abstract
Partial Combinatory Algebras (PCAs) provide a foundational model of the untyped λ-calculus and serve as the basis for many notions of computability, such as realizability theory. However, PCAs support a very limited notion of computation by only incorporating non-termination as a computational effect. To provide a framework that better internalizes a wide range of computational effects, this paper puts forward the notion of Monadic Combinatory Algebras (MCAs). MCAs generalize the notion of PCAs by structuring the combinatory algebra over an underlying computational effect, embodied by a monad. We show that MCAs can support various side effects through the underlying monad, such as non-determinism, stateful computation and continuations. We further obtain a categorical characterization of MCAs within Freyd Categories, following a similar connection for PCAs. Moreover, we explore the application of MCAs in realizability theory, presenting constructions of effectful realizability triposes and assemblies derived through evidenced frames, thereby generalizing traditional PCA-based realizability semantics. The monadic generalization of the foundational notion of PCAs provides a comprehensive and powerful framework for internally reasoning about effectful computations, paving the path to a more encompassing study of computation and its relationship with realizability models and programming languages.
Cite as

Liron Cohen, Ariel Grunfeld, Dominik Kirst, and Étienne Miquey. From Partial to Monadic: Combinatory Algebra with Effects. In 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 337, pp. 14:1-14:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{cohen_et_al:LIPIcs.FSCD.2025.14,
  author =	{Cohen, Liron and Grunfeld, Ariel and Kirst, Dominik and Miquey, \'{E}tienne},
  title =	{{From Partial to Monadic: Combinatory Algebra with Effects}},
  booktitle =	{10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)},
  pages =	{14:1--14:22},
  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.2025.14},
  URN =		{urn:nbn:de:0030-drops-236297},
  doi =		{10.4230/LIPIcs.FSCD.2025.14},
  annote =	{Keywords: Combinatory algebras, Monads, Effects, Realizability, Evidenced frames}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2023.37
Inductive Continuity via Brouwer Trees

Authors: Liron Cohen, Bruno da Rocha Paiva, Vincent Rahli, and Ayberk Tosun

Published in: LIPIcs, Volume 272, 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)

Abstract
Continuity is a key principle of intuitionistic logic that is generally accepted by constructivists but is inconsistent with classical logic. Most commonly, continuity states that a function from the Baire space to numbers, only needs approximations of the points in the Baire space to compute. More recently, another formulation of the continuity principle was put forward. It states that for any function F from the Baire space to numbers, there exists a (dialogue) tree that contains the values of F at its leaves and such that the modulus of F at each point of the Baire space is given by the length of the corresponding branch in the tree. In this paper we provide the first internalization of this "inductive" continuity principle within a computational setting. Concretely, we present a class of intuitionistic theories that validate this formulation of continuity thanks to computations that construct such dialogue trees internally to the theories using effectful computations. We further demonstrate that this inductive continuity principle implies other forms of continuity principles.
Cite as

Liron Cohen, Bruno da Rocha Paiva, Vincent Rahli, and Ayberk Tosun. Inductive Continuity via Brouwer Trees. In 48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 272, pp. 37:1-37:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{cohen_et_al:LIPIcs.MFCS.2023.37,
  author =	{Cohen, Liron and da Rocha Paiva, Bruno and Rahli, Vincent and Tosun, Ayberk},
  title =	{{Inductive Continuity via Brouwer Trees}},
  booktitle =	{48th International Symposium on Mathematical Foundations of Computer Science (MFCS 2023)},
  pages =	{37:1--37:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-292-1},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{272},
  editor =	{Leroux, J\'{e}r\^{o}me and Lombardy, Sylvain and Peleg, David},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2023.37},
  URN =		{urn:nbn:de:0030-drops-185718},
  doi =		{10.4230/LIPIcs.MFCS.2023.37},
  annote =	{Keywords: Continuity, Dialogue trees, Stateful computations, Intuitionistic Logic, Extensional Type Theory, Constructive Type Theory, Realizability, Theorem proving, Agda}
}
Document
DOI: 10.4230/LIPIcs.CSL.2023.15
Realizing Continuity Using Stateful Computations

Authors: Liron Cohen and Vincent Rahli

Published in: LIPIcs, Volume 252, 31st EACSL Annual Conference on Computer Science Logic (CSL 2023)

Abstract
The principle of continuity is a seminal property that holds for a number of intuitionistic theories such as System T. Roughly speaking, it states that functions on real numbers only need approximations of these numbers to compute. Generally, continuity principles have been justified using semantical arguments, but it is known that the modulus of continuity of functions can be computed using effectful computations such as exceptions or reference cells. This paper presents a class of intuitionistic theories that features stateful computations, such as reference cells, and shows that these theories can be extended with continuity axioms. The modulus of continuity of the functionals on the Baire space is directly computed using the stateful computations enabled in the theory.
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Liron Cohen and Vincent Rahli. Realizing Continuity Using Stateful Computations. In 31st EACSL Annual Conference on Computer Science Logic (CSL 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 252, pp. 15:1-15:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{cohen_et_al:LIPIcs.CSL.2023.15,
  author =	{Cohen, Liron and Rahli, Vincent},
  title =	{{Realizing Continuity Using Stateful Computations}},
  booktitle =	{31st EACSL Annual Conference on Computer Science Logic (CSL 2023)},
  pages =	{15:1--15:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-264-8},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{252},
  editor =	{Klin, Bartek and Pimentel, Elaine},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2023.15},
  URN =		{urn:nbn:de:0030-drops-174761},
  doi =		{10.4230/LIPIcs.CSL.2023.15},
  annote =	{Keywords: Continuity, Stateful computations, Intuitionism, Extensional Type Theory, Constructive Type Theory, Realizability, Theorem proving, Agda}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2022.10
Constructing Unprejudiced Extensional Type Theories with Choices via Modalities

Authors: Liron Cohen and Vincent Rahli

Published in: LIPIcs, Volume 228, 7th International Conference on Formal Structures for Computation and Deduction (FSCD 2022)

Abstract
Time-progressing expressions, i.e., expressions that compute to different values over time such as Brouwerian choice sequences or reference cells, are a common feature in many frameworks. For type theories to support such elements, they usually employ sheaf models. In this paper, we provide a general framework in the form of an extensional type theory incorporating various time-progressing elements along with a general possible-worlds forcing interpretation parameterized by modalities. The modalities can, in turn, be instantiated with topological spaces of bars, leading to a general sheaf model. This parameterized construction allows us to capture a distinction between theories that are "agnostic", i.e., compatible with classical reasoning in the sense that classical axioms can be validated, and those that are "intuitionistic", i.e., incompatible with classical reasoning in the sense that classical axioms can be proven false. This distinction is made via properties of the modalities selected to model the theory and consequently via the space of bars instantiating the modalities. We further identify a class of time-progressing elements that allows deriving "intuitionistic" theories that include not only choice sequences but also simpler operators, namely reference cells.
Cite as

Liron Cohen and Vincent Rahli. Constructing Unprejudiced Extensional Type Theories with Choices via Modalities. In 7th International Conference on Formal Structures for Computation and Deduction (FSCD 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 228, pp. 10:1-10:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{cohen_et_al:LIPIcs.FSCD.2022.10,
  author =	{Cohen, Liron and Rahli, Vincent},
  title =	{{Constructing Unprejudiced Extensional Type Theories with Choices via Modalities}},
  booktitle =	{7th International Conference on Formal Structures for Computation and Deduction (FSCD 2022)},
  pages =	{10:1--10:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-233-4},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{228},
  editor =	{Felty, Amy P.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2022.10},
  URN =		{urn:nbn:de:0030-drops-162917},
  doi =		{10.4230/LIPIcs.FSCD.2022.10},
  annote =	{Keywords: Intuitionism, Extensional Type Theory, Constructive Type Theory, Realizability, Choice sequences, References, Classical Logic, Theorem proving, Agda}
}
Document
Complete Volume
DOI: 10.4230/LIPIcs.ITP.2021
LIPIcs, Volume 193, ITP 2021, Complete Volume

Authors: Liron Cohen and Cezary Kaliszyk

Published in: LIPIcs, Volume 193, 12th International Conference on Interactive Theorem Proving (ITP 2021)

Abstract
LIPIcs, Volume 193, ITP 2021, Complete Volume
Cite as

12th International Conference on Interactive Theorem Proving (ITP 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 193, pp. 1-560, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@Proceedings{cohen_et_al:LIPIcs.ITP.2021,
  title =	{{LIPIcs, Volume 193, ITP 2021, Complete Volume}},
  booktitle =	{12th International Conference on Interactive Theorem Proving (ITP 2021)},
  pages =	{1--560},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-188-7},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{193},
  editor =	{Cohen, Liron and Kaliszyk, Cezary},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITP.2021},
  URN =		{urn:nbn:de:0030-drops-138943},
  doi =		{10.4230/LIPIcs.ITP.2021},
  annote =	{Keywords: LIPIcs, Volume 193, ITP 2021, Complete Volume}
}
Document
Front Matter
DOI: 10.4230/LIPIcs.ITP.2021.0
Front Matter, Table of Contents, Preface, Conference Organization

Authors: Liron Cohen and Cezary Kaliszyk

Published in: LIPIcs, Volume 193, 12th International Conference on Interactive Theorem Proving (ITP 2021)

Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as

12th International Conference on Interactive Theorem Proving (ITP 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 193, pp. 0:i-0:viii, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{cohen_et_al:LIPIcs.ITP.2021.0,
  author =	{Cohen, Liron and Kaliszyk, Cezary},
  title =	{{Front Matter, Table of Contents, Preface, Conference Organization}},
  booktitle =	{12th International Conference on Interactive Theorem Proving (ITP 2021)},
  pages =	{0:i--0:viii},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-188-7},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{193},
  editor =	{Cohen, Liron and Kaliszyk, Cezary},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITP.2021.0},
  URN =		{urn:nbn:de:0030-drops-138955},
  doi =		{10.4230/LIPIcs.ITP.2021.0},
  annote =	{Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
DOI: 10.4230/LIPIcs.CSL.2021.11
Open Bar - a Brouwerian Intuitionistic Logic with a Pinch of Excluded Middle

Authors: Mark Bickford, Liron Cohen, Robert L. Constable, and Vincent Rahli

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

Abstract
One of the differences between Brouwerian intuitionistic logic and classical logic is their treatment of time. In classical logic truth is atemporal, whereas in intuitionistic logic it is time-relative. Thus, in intuitionistic logic it is possible to acquire new knowledge as time progresses, whereas the classical Law of Excluded Middle (LEM) is essentially flattening the notion of time stating that it is possible to decide whether or not some knowledge will ever be acquired. This paper demonstrates that, nonetheless, the two approaches are not necessarily incompatible by introducing an intuitionistic type theory along with a Beth-like model for it that provide some middle ground. On one hand they incorporate a notion of progressing time and include evolving mathematical entities in the form of choice sequences, and on the other hand they are consistent with a variant of the classical LEM. Accordingly, this new type theory provides the basis for a more classically inclined Brouwerian intuitionistic type theory.
Cite as

Mark Bickford, Liron Cohen, Robert L. Constable, and Vincent Rahli. Open Bar - a Brouwerian Intuitionistic Logic with a Pinch of Excluded Middle. In 29th EACSL Annual Conference on Computer Science Logic (CSL 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 183, pp. 11:1-11:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{bickford_et_al:LIPIcs.CSL.2021.11,
  author =	{Bickford, Mark and Cohen, Liron and Constable, Robert L. and Rahli, Vincent},
  title =	{{Open Bar - a Brouwerian Intuitionistic Logic with a Pinch of Excluded Middle}},
  booktitle =	{29th EACSL Annual Conference on Computer Science Logic (CSL 2021)},
  pages =	{11:1--11:23},
  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.2021.11},
  URN =		{urn:nbn:de:0030-drops-134455},
  doi =		{10.4230/LIPIcs.CSL.2021.11},
  annote =	{Keywords: Intuitionism, Extensional type theory, Constructive Type Theory, Realizability, Choice sequences, Classical Logic, Law of Excluded Middle, Theorem proving, Coq}
}
Document
DOI: 10.4230/LIPIcs.CSL.2018.17
Uniform Inductive Reasoning in Transitive Closure Logic via Infinite Descent

Authors: Liron Cohen and Reuben N. S. Rowe

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

Abstract
Transitive closure logic is a known extension of first-order logic obtained by introducing a transitive closure operator. While other extensions of first-order logic with inductive definitions are a priori parametrized by a set of inductive definitions, the addition of the transitive closure operator uniformly captures all finitary inductive definitions. In this paper we present an infinitary proof system for transitive closure logic which is an infinite descent-style counterpart to the existing (explicit induction) proof system for the logic. We show that, as for similar systems for first-order logic with inductive definitions, our infinitary system is complete for the standard semantics and subsumes the explicit system. Moreover, the uniformity of the transitive closure operator allows semantically meaningful complete restrictions to be defined using simple syntactic criteria. Consequently, the restriction to regular infinitary (i.e. cyclic) proofs provides the basis for an effective system for automating inductive reasoning.
Cite as

Liron Cohen and Reuben N. S. Rowe. Uniform Inductive Reasoning in Transitive Closure Logic via Infinite Descent. In 27th EACSL Annual Conference on Computer Science Logic (CSL 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 119, pp. 17:1-17:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{cohen_et_al:LIPIcs.CSL.2018.17,
  author =	{Cohen, Liron and Rowe, Reuben N. S.},
  title =	{{Uniform Inductive Reasoning in Transitive Closure Logic via Infinite Descent}},
  booktitle =	{27th EACSL Annual Conference on Computer Science Logic (CSL 2018)},
  pages =	{17:1--17:16},
  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.2018.17},
  URN =		{urn:nbn:de:0030-drops-96841},
  doi =		{10.4230/LIPIcs.CSL.2018.17},
  annote =	{Keywords: Induction, Transitive Closure, Infinitary Proof Systems, Cyclic Proof Systems, Soundness, Completeness, Standard Semantics, Henkin Semantics}
}
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