DROPS

Document

DOI: 10.4230/LIPIcs.ITCS.2026.86

The Secretary Problem with Predictions and a Chosen Order

Authors: Helia Karisani, Mohammadreza Daneshvaramoli, Hedyeh Beyhaghi, Mohammad Hajiesmaili, and Cameron Musco

Published in: LIPIcs, Volume 362, 17th Innovations in Theoretical Computer Science Conference (ITCS 2026)

Abstract

We study a learning-augmented variant of the secretary problem, recently introduced by Fujii and Yoshida (2023). In this variant, the decision-maker has access to machine-learned predictions of candidate values in advance. The key challenge is to balance consistency and robustness: when the predictions are accurate, the algorithm should hire a near-best secretary; however, if they are inaccurate, the algorithm should still achieve a bounded competitive ratio. We consider both the standard Random Order Secretary Problem (ROSP), where candidates arrive in a uniform random order, and a more natural model in the learning-augmented setting, where the decision-maker can choose the arrival order based on the predicted candidate values. This model, which we call the Chosen Order Secretary Problem (COSP), can capture scenarios such as an interview schedule that is set by the decision-maker. We propose a novel algorithm that applies to both ROSP and COSP. Building on the approach of Fujii and Yoshida, our method switches from fully trusting predictions to a threshold-based rule when a large deviation of a prediction is observed. Importantly, unlike the algorithm of Fujii and Yoshida, our algorithm uses randomization as part of its decision logic. We show that if ε ∈ [0,1] denotes the maximum multiplicative prediction error, then for ROSP our algorithm achieves competitive ratio max {0.221, (1-ε)/(1+ε)}, improving on a previous bound of max {0.215, (1-ε)/(1+ε)} due to Fujii and Yoshida [Fujii and Yoshida, 2023]. For COSP, our algorithm achieves max {0.262, (1-ε)/(1+ε)}. This surpasses a 0.25 upper bound on the worst-case competitive ratio that applies to the approach of Fujii and Yoshida, and gets closer to the classical secretary benchmark of 1/e ≈ 0.368, which is an upper bound for any algorithm. Our result for COSP highlights the benefit of integrating predictions with arrival-order control in online decision-making.

Cite as

Helia Karisani, Mohammadreza Daneshvaramoli, Hedyeh Beyhaghi, Mohammad Hajiesmaili, and Cameron Musco. The Secretary Problem with Predictions and a Chosen Order. In 17th Innovations in Theoretical Computer Science Conference (ITCS 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 362, pp. 86:1-86:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{karisani_et_al:LIPIcs.ITCS.2026.86,
  author =	{Karisani, Helia and Daneshvaramoli, Mohammadreza and Beyhaghi, Hedyeh and Hajiesmaili, Mohammad and Musco, Cameron},
  title =	{{The Secretary Problem with Predictions and a Chosen Order}},
  booktitle =	{17th Innovations in Theoretical Computer Science Conference (ITCS 2026)},
  pages =	{86:1--86:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-410-9},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{362},
  editor =	{Saraf, Shubhangi},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2026.86},
  URN =		{urn:nbn:de:0030-drops-253734},
  doi =		{10.4230/LIPIcs.ITCS.2026.86},
  annote =	{Keywords: Secretary problem, learning-augmented algorithms, online algorithms}
}

Document

DOI: 10.4230/LIPIcs.FSTTCS.2025.52

Unreliability in Practical Subclasses of Communicating Systems

Authors: Amrita Suresh and Nobuko Yoshida

Published in: LIPIcs, Volume 360, 45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025)

Abstract

Systems of communicating automata are prominent models for peer-to-peer message-passing over unbounded channels, but in the general scenario, most verification properties are undecidable. To address this issue, two decidable subclasses, Realisable with Synchronous Communication (RSC) and k-Multiparty Compatibility (k-MC), were proposed in the literature, with corresponding verification tools developed and applied in practice. Unfortunately, both RSC and k-MC are not resilient under failures: (1) their decidability relies on the assumption of perfect channels and (2) most standard protocols do not satisfy RSC or k-MC under failures. To address these limitations, this paper studies the resilience of RSC and k-MC under two distinct failure models: interference and crash-stop failures. For interference, we relax the conditions of RSC and k-MC and prove that the inclusions of these relaxed properties remain decidable under interference, preserving their known complexity bounds. We then propose a novel crash-handling communicating system that captures wider behaviours than existing multiparty session types (MPST) with crash-stop failures. We study a translation of MPST with crash-stop failures into this system integrating RSC and k-MC properties, and establish their decidability results. Finally, by verifying representative protocols from the literature using RSC and k-MC tools extended to interferences, we evaluate the relaxed systems and demonstrate their resilience.

Cite as

Amrita Suresh and Nobuko Yoshida. Unreliability in Practical Subclasses of Communicating Systems. In 45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 360, pp. 52:1-52:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{suresh_et_al:LIPIcs.FSTTCS.2025.52,
  author =	{Suresh, Amrita and Yoshida, Nobuko},
  title =	{{Unreliability in Practical Subclasses of Communicating Systems}},
  booktitle =	{45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025)},
  pages =	{52:1--52:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-406-2},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{360},
  editor =	{Aiswarya, C. and Mehta, Ruta and Roy, Subhajit},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2025.52},
  URN =		{urn:nbn:de:0030-drops-251312},
  doi =		{10.4230/LIPIcs.FSTTCS.2025.52},
  annote =	{Keywords: Communicating automata, lossy channel, corruption, out of order, session types, crash-stop failure}
}

Document

DOI: 10.4230/LIPIcs.ITP.2025.13

Barendregt’s Theory of the λ-Calculus, Refreshed and Formalized

Authors: Adrienne Lancelot, Beniamino Accattoli, and Maxime Vemclefs

Published in: LIPIcs, Volume 352, 16th International Conference on Interactive Theorem Proving (ITP 2025)

Abstract

Barendregt’s book on the untyped λ-calculus refines the inconsistent view of β-divergence as representation of the undefined via the key concept of head reduction. In this paper, we put together recent revisitations of some key theorems laid out in Barendregt’s book, and we formalize them in the Abella proof assistant. Our work provides a compact and refreshed presentation of the core of the book. The formalization faithfully mimics pen-and-paper proofs. Two interesting aspects are the manipulation of contexts for the study of contextual equivalence and a formal alternative to the informal trick at work in Takahashi’s proof of the genericity lemma. As a by-product, we obtain an alternative definition of contextual equivalence that does not mention contexts.

Cite as

Adrienne Lancelot, Beniamino Accattoli, and Maxime Vemclefs. Barendregt’s Theory of the λ-Calculus, Refreshed and Formalized. In 16th International Conference on Interactive Theorem Proving (ITP 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 352, pp. 13:1-13:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{lancelot_et_al:LIPIcs.ITP.2025.13,
  author =	{Lancelot, Adrienne and Accattoli, Beniamino and Vemclefs, Maxime},
  title =	{{Barendregt’s Theory of the \lambda-Calculus, Refreshed and Formalized}},
  booktitle =	{16th International Conference on Interactive Theorem Proving (ITP 2025)},
  pages =	{13:1--13:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-396-6},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{352},
  editor =	{Forster, Yannick and Keller, Chantal},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITP.2025.13},
  URN =		{urn:nbn:de:0030-drops-246114},
  doi =		{10.4230/LIPIcs.ITP.2025.13},
  annote =	{Keywords: lambda-calculus, head reduction, equational theory}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2025.11

A Sound and Complete Characterization of Fair Asynchronous Session Subtyping

Authors: Mario Bravetti, Luca Padovani, and Gianluigi Zavattaro

Published in: LIPIcs, Volume 348, 36th International Conference on Concurrency Theory (CONCUR 2025)

Abstract

Session types are abstractions of communication protocols enabling the static analysis of message-passing processes. Refinement notions for session types are key to support safe forms of process substitution while preserving their compatibility with the rest of the system. Recently, a fair refinement relation for asynchronous session types has been defined allowing the anticipation of message outputs with respect to an unbounded number of message inputs. This refinement is useful to capture common patterns in communication protocols that take advantage of asynchrony. However, while the semantic (à la testing) definition of such refinement is straightforward, its characterization has proved to be quite challenging. In fact, only a sound but not complete characterization is known so far. In this paper we close this open problem by presenting a sound and complete characterization of asynchronous fair refinement for session types. We relate this characterization to those given in the literature for synchronous session types by leveraging a novel labelled transition system of session types that embeds their asynchronous semantics.

Cite as

Mario Bravetti, Luca Padovani, and Gianluigi Zavattaro. A Sound and Complete Characterization of Fair Asynchronous Session Subtyping. In 36th International Conference on Concurrency Theory (CONCUR 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 348, pp. 11:1-11:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{bravetti_et_al:LIPIcs.CONCUR.2025.11,
  author =	{Bravetti, Mario and Padovani, Luca and Zavattaro, Gianluigi},
  title =	{{A Sound and Complete Characterization of Fair Asynchronous Session Subtyping}},
  booktitle =	{36th International Conference on Concurrency Theory (CONCUR 2025)},
  pages =	{11:1--11:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-389-8},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{348},
  editor =	{Bouyer, Patricia and van de Pol, Jaco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2025.11},
  URN =		{urn:nbn:de:0030-drops-239615},
  doi =		{10.4230/LIPIcs.CONCUR.2025.11},
  annote =	{Keywords: Binary sessions, session types, fair asynchronous subtyping}
}

Document

DOI: 10.4230/LIPIcs.FSCD.2025.4

Substructural Parametricity

Authors: C. B. Aberlé, Karl Crary, Chris Martens, and Frank Pfenning

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

Abstract

Ordered, linear, and other substructural type systems allow us to expose deep properties of programs at the syntactic level of types. In this paper, we develop a family of unary logical relations that allow us to prove consequences of parametricity for a range of substructural type systems. A key idea is to parameterize the relation by an algebra, which we exemplify with a monoid and commutative monoid to interpret ordered and linear type systems, respectively. We prove the fundamental theorem of logical relations and apply it to deduce extensional properties of inhabitants of certain types. Examples include demonstrating that the ordered types for list append and reversal are inhabited by exactly one function, as are types of some tree traversals. Similarly, the linear type of the identity function on lists is inhabited only by permutations of the input. Our most advanced example shows that the ordered type of the list fold function is inhabited only by the fold function.

Cite as

C. B. Aberlé, Karl Crary, Chris Martens, and Frank Pfenning. Substructural Parametricity. In 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 337, pp. 4:1-4:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{aberle_et_al:LIPIcs.FSCD.2025.4,
  author =	{Aberl\'{e}, C. B. and Crary, Karl and Martens, Chris and Pfenning, Frank},
  title =	{{Substructural Parametricity}},
  booktitle =	{10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)},
  pages =	{4:1--4:21},
  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.2025.4},
  URN =		{urn:nbn:de:0030-drops-236193},
  doi =		{10.4230/LIPIcs.FSCD.2025.4},
  annote =	{Keywords: Substructural type systems, logical relations, ordered logic}
}

Document

DOI: 10.4230/LIPIcs.FSCD.2025.7

Combining Generalization Algorithms in Regular Collapse-Free Theories

Authors: Mauricio Ayala-Rincón, David M. Cerna, Temur Kutsia, and Christophe Ringeissen

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

Abstract

We look at the generalization problem modulo some equational theories. This problem is dual to the unification problem: given two input terms, we want to find a common term whose respective two instances are equivalent to the original terms modulo the theory. There exist algorithms for finding generalizations over various equational theories. We focus on modular construction of equational generalization algorithms for the union of signature-disjoint theories. Specifically, we consider the class of regular and collapse-free theories, showing how to combine existing generalization algorithms to produce specific solutions in these cases. Additionally, we identify a class of theories that admit a generalization algorithm based on the application of axioms to resolve the problem. To define this class, we rely on the notion of syntactic theories, a concept originally introduced to develop unification procedures similar to the one known for syntactic unification. We demonstrate that syntactic theories are also helpful in developing generalization procedures similar to those used for syntactic generalization.

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Mauricio Ayala-Rincón, David M. Cerna, Temur Kutsia, and Christophe Ringeissen. Combining Generalization Algorithms in Regular Collapse-Free Theories. In 10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 337, pp. 7:1-7:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{ayalarincon_et_al:LIPIcs.FSCD.2025.7,
  author =	{Ayala-Rinc\'{o}n, Mauricio and Cerna, David M. and Kutsia, Temur and Ringeissen, Christophe},
  title =	{{Combining Generalization Algorithms in Regular Collapse-Free Theories}},
  booktitle =	{10th International Conference on Formal Structures for Computation and Deduction (FSCD 2025)},
  pages =	{7:1--7:18},
  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.2025.7},
  URN =		{urn:nbn:de:0030-drops-236228},
  doi =		{10.4230/LIPIcs.FSCD.2025.7},
  annote =	{Keywords: Generalization, Anti-unification, Equational theories, Combination}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2025.30

In-Memory Object Graph Stores

Authors: Aditya Thimmaiah, Zijian Yi, Joseph Kenis, Christopher J Rossbach, and Milos Gligoric

Published in: LIPIcs, Volume 333, 39th European Conference on Object-Oriented Programming (ECOOP 2025)

Abstract

We present a design and implementation of an in-memory object graph store, dubbed εStore. Our key innovation is a storage model - epsilon store - that equates an object on the heap to a node in a graph store. Thus any object on the heap (without changes) can be a part of one, or multiple, graph stores, and vice versa, any node in a graph store can be accessed like any other object on the heap. Specifically, each node in a graph is an object (i.e., instance of a class), and its properties and its edges are the primitive and reference fields declared in its class, respectively. Necessary classes, which are instantiated to represent nodes, are created dynamically by εStore. εStore uses a subset of the Cypher query language to query the graph store. By design, the result of any query is a table (ResultSet) of references to objects on the heap, which users can manipulate the same way as any other object on the heap in their programs. Moreover, a developer can include (transitively) an arbitrary object to become a part of a graph store. Finally, εStore introduces compile-time rewriting of Cypher queries into imperative code to improve the runtime performance. εStore can be used for a number of tasks including implementing methods for complex in-memory structures, writing complex assertions, or a stripped down version of a graph database that can conveniently be used during testing. We implement εStore in Java and show its application using the aforementioned tasks.

Cite as

Aditya Thimmaiah, Zijian Yi, Joseph Kenis, Christopher J Rossbach, and Milos Gligoric. In-Memory Object Graph Stores. In 39th European Conference on Object-Oriented Programming (ECOOP 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 333, pp. 30:1-30:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{thimmaiah_et_al:LIPIcs.ECOOP.2025.30,
  author =	{Thimmaiah, Aditya and Yi, Zijian and Kenis, Joseph and Rossbach, Christopher J and Gligoric, Milos},
  title =	{{In-Memory Object Graph Stores}},
  booktitle =	{39th European Conference on Object-Oriented Programming (ECOOP 2025)},
  pages =	{30:1--30:30},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-373-7},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{333},
  editor =	{Aldrich, Jonathan 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.ECOOP.2025.30},
  URN =		{urn:nbn:de:0030-drops-233225},
  doi =		{10.4230/LIPIcs.ECOOP.2025.30},
  annote =	{Keywords: Object stores, Graph stores, Cypher}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2025.24

Fair Termination of Asynchronous Binary Sessions

Authors: Luca Padovani and Gianluigi Zavattaro

Published in: LIPIcs, Volume 333, 39th European Conference on Object-Oriented Programming (ECOOP 2025)

Abstract

We study a theory of asynchronous session types ensuring that well-typed processes terminate under a suitable fairness assumption. Fair termination entails starvation freedom and orphan message freedom namely that all messages, including those that are produced early taking advantage of asynchrony, are eventually consumed. The theory is based on a novel fair asynchronous subtyping relation for session types that is coarser than the existing ones. The type system is also the first of its kind that is firmly rooted in linear logic: fair asynchronous subtyping is incorporated as a natural generalization of the cut and axiom rules of linear logic and asynchronous communication is modeled through a suitable set of commuting conversions and of deep cut reductions in linear logic proofs.

Cite as

Luca Padovani and Gianluigi Zavattaro. Fair Termination of Asynchronous Binary Sessions. In 39th European Conference on Object-Oriented Programming (ECOOP 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 333, pp. 24:1-24:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{padovani_et_al:LIPIcs.ECOOP.2025.24,
  author =	{Padovani, Luca and Zavattaro, Gianluigi},
  title =	{{Fair Termination of Asynchronous Binary Sessions}},
  booktitle =	{39th European Conference on Object-Oriented Programming (ECOOP 2025)},
  pages =	{24:1--24:29},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-373-7},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{333},
  editor =	{Aldrich, Jonathan 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.ECOOP.2025.24},
  URN =		{urn:nbn:de:0030-drops-233169},
  doi =		{10.4230/LIPIcs.ECOOP.2025.24},
  annote =	{Keywords: Binary sessions, fair asynchronous subtyping, fair termination, linear logic}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2025.17

Contrasting Deadlock-Free Session Processes

Authors: Juan C. Jaramillo and Jorge A. Pérez

Published in: LIPIcs, Volume 333, 39th European Conference on Object-Oriented Programming (ECOOP 2025)

Abstract

Deadlock freedom is a crucial property for message-passing programs. Over the years, several different type systems for concurrent processes that ensure deadlock freedom have been proposed; this diversity raises the question of how they compare. We address this question, considering two type systems not covered in prior work: Kokke et al.’s HCP, a type system based on a linear logic with hypersequents, and Padovani’s priority-based type system for asynchronous processes, dubbed 𝖯. Their distinctive features make formal comparisons relevant and challenging. Our findings are two-fold: (1) the hypersequent setting does not drastically change the class of deadlock-free processes induced by linear logic, and (2) we relate the classes of deadlock-free processes induced by HCP and 𝖯. We prove that our results hold under both synchronous and asynchronous communication. Our results provide new insights into the essential mechanisms involved in statically avoiding deadlocks in concurrency.

Cite as

Juan C. Jaramillo and Jorge A. Pérez. Contrasting Deadlock-Free Session Processes. In 39th European Conference on Object-Oriented Programming (ECOOP 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 333, pp. 17:1-17:29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{jaramillo_et_al:LIPIcs.ECOOP.2025.17,
  author =	{Jaramillo, Juan C. and P\'{e}rez, Jorge A.},
  title =	{{Contrasting Deadlock-Free Session Processes}},
  booktitle =	{39th European Conference on Object-Oriented Programming (ECOOP 2025)},
  pages =	{17:1--17:29},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-373-7},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{333},
  editor =	{Aldrich, Jonathan 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.ECOOP.2025.17},
  URN =		{urn:nbn:de:0030-drops-233103},
  doi =		{10.4230/LIPIcs.ECOOP.2025.17},
  annote =	{Keywords: session types, process calculi, deadlock freedom}
}

Document

DOI: 10.4230/OASIcs.FMBC.2025.10

Program Logics for Ledgers

Authors: Orestis Melkonian, Wouter Swierstra, and James Chapman

Published in: OASIcs, Volume 129, 6th International Workshop on Formal Methods for Blockchains (FMBC 2025)

Abstract

Distributed ledgers nowadays manage substantial monetary funds in the form of cryptocurrencies such as Bitcoin, Ethereum, and Cardano. For such ledgers to be safe, operations that add new entries must be cryptographically sound - but it is less clear how to reason effectively about such ever-growing linear data structures. This paper demonstrates how distributed ledgers may be viewed as computer programs, that, when executed, transfer funds between various parties. As a result, familiar program logics, such as Hoare logic, are applied in a novel setting. Borrowing ideas from concurrent separation logic, this enables modular reasoning principles over arbitrary fragments of any ledger. All of our results have been mechanised in the Agda proof assistant.

Cite as

Orestis Melkonian, Wouter Swierstra, and James Chapman. Program Logics for Ledgers. In 6th International Workshop on Formal Methods for Blockchains (FMBC 2025). Open Access Series in Informatics (OASIcs), Volume 129, pp. 10:1-10:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{melkonian_et_al:OASIcs.FMBC.2025.10,
  author =	{Melkonian, Orestis and Swierstra, Wouter and Chapman, James},
  title =	{{Program Logics for Ledgers}},
  booktitle =	{6th International Workshop on Formal Methods for Blockchains (FMBC 2025)},
  pages =	{10:1--10:22},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-371-3},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{129},
  editor =	{Marmsoler, Diego and Xu, Meng},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.FMBC.2025.10},
  URN =		{urn:nbn:de:0030-drops-230370},
  doi =		{10.4230/OASIcs.FMBC.2025.10},
  annote =	{Keywords: blockchain, distributed ledgers, UTxO separation logic, program semantics, formal verification, Agda}
}

Document

DOI: 10.4230/LIPIcs.CSL.2025.32

A Mixed Linear and Graded Logic: Proofs, Terms, and Models

Authors: Victoria Vollmer, Danielle Marshall, Harley Eades III, and Dominic Orchard

Published in: LIPIcs, Volume 326, 33rd EACSL Annual Conference on Computer Science Logic (CSL 2025)

Abstract

Graded modal logics generalise standard modal logics via families of modalities indexed by an algebraic structure whose operations mediate between the different modalities. The graded "of-course" modality !_r captures how many times a proposition is used and has an analogous interpretation to the of-course modality from linear logic; the of-course modality from linear logic can be modelled by a linear exponential comonad and graded of-course can be modelled by a graded linear exponential comonad. Benton showed in his seminal paper on Linear/Non-Linear logic that the of-course modality can be split into two modalities connecting intuitionistic logic with linear logic, forming a symmetric monoidal adjunction. Later, Fujii et al. demonstrated that every graded comonad can be decomposed into an adjunction and a "strict action". We give a similar result to Benton, leveraging Fujii et al.’s decomposition, showing that graded modalities can be split into two modalities connecting a graded logic with a graded linear logic. We propose a sequent calculus, its proof theory and categorical model, and a natural deduction system which we show is isomorphic to the sequent calculus system. Interestingly, our system can also be understood as Linear/Non-Linear logic composed with an action that adds the grading, further illuminating the shared principles between linear logic and a class of graded modal logics.

Cite as

Victoria Vollmer, Danielle Marshall, Harley Eades III, and Dominic Orchard. A Mixed Linear and Graded Logic: Proofs, Terms, and Models. In 33rd EACSL Annual Conference on Computer Science Logic (CSL 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 326, pp. 32:1-32:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{vollmer_et_al:LIPIcs.CSL.2025.32,
  author =	{Vollmer, Victoria and Marshall, Danielle and Eades III, Harley and Orchard, Dominic},
  title =	{{A Mixed Linear and Graded Logic: Proofs, Terms, and Models}},
  booktitle =	{33rd EACSL Annual Conference on Computer Science Logic (CSL 2025)},
  pages =	{32:1--32:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-362-1},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{326},
  editor =	{Endrullis, J\"{o}rg and Schmitz, Sylvain},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2025.32},
  URN =		{urn:nbn:de:0030-drops-227892},
  doi =		{10.4230/LIPIcs.CSL.2025.32},
  annote =	{Keywords: linear logic, graded modal logic, adjoint decomposition}
}

Document

DOI: 10.4230/OASIcs.Tannen.4

Annotation and More Annotation: Some Problems Posed by (and to) Val Tannen

Authors: Peter Buneman and Stijn Vansummeren

Published in: OASIcs, Volume 119, The Provenance of Elegance in Computation - Essays Dedicated to Val Tannen (2024)

Abstract

Among the many research accomplishments of Val Tannen, his work on provenance and semirings is probably the most widely known. In this paper, we discuss questions that arise when applying this general framework to the setting of curated databases, and in particular the setting where we can have multiple annotations on the same data, as well as annotations on annotations.

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Peter Buneman and Stijn Vansummeren. Annotation and More Annotation: Some Problems Posed by (and to) Val Tannen. In The Provenance of Elegance in Computation - Essays Dedicated to Val Tannen. Open Access Series in Informatics (OASIcs), Volume 119, pp. 4:1-4:8, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{buneman_et_al:OASIcs.Tannen.4,
  author =	{Buneman, Peter and Vansummeren, Stijn},
  title =	{{Annotation and More Annotation: Some Problems Posed by (and to) Val Tannen}},
  booktitle =	{The Provenance of Elegance in Computation - Essays Dedicated to Val Tannen},
  pages =	{4:1--4:8},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-320-1},
  ISSN =	{2190-6807},
  year =	{2024},
  volume =	{119},
  editor =	{Amarilli, Antoine and Deutsch, Alin},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Tannen.4},
  URN =		{urn:nbn:de:0030-drops-201007},
  doi =		{10.4230/OASIcs.Tannen.4},
  annote =	{Keywords: Annotation, provenance, semiring, curated data}
}

Document

DOI: 10.4230/DagRep.11.8.52

Behavioural Types: Bridging Theory and Practice (Dagstuhl Seminar 21372)

Authors: Mariangiola Dezani, Roland Kuhn, Sam Lindley, and Alceste Scalas

Published in: Dagstuhl Reports, Volume 11, Issue 8 (2022)

Abstract

Behavioural types specify the way in which software components interact with one another. Unlike data types (which describe the structure of data), behavioural types describe communication protocols, and their verification ensures that programs do not violate such protocols. The behavioural types research community has developed a flourishing literature on communication-centric programming, exploring many directions. One of the most studied behavioural type systems are session types, introduced by Honda et al. in the ‘90s, and awarded with prizes for their influence in the past 20 and 10 years (by the ESOP and POPL conferences, respectively). Other varieties of behavioural types include typestate systems, choreographies, and behavioural contracts; research on verification techniques covers the spectrum from fully static verification at compile-time to fully dynamic verification at run-time. In the last decade, research on behavioural types has shifted emphasis towards practical applications, using both novel and existing programming languages (e.g., Java, Python, Go, C, Haskell, OCaml, Erlang, Scala, Rust). An earlier Dagstuhl Seminar, 17051 "Theory and Applications of Behavioural Types" (January 29-February 3, 2017), played an important role in coordinating this effort. Yet, despite the vibrant community and the stream of new results, the use of behavioural types for mainstream software development and verification remains limited. This limitation is largely down to the rapid pace at which mainstream industrial practice for the design and development of concurrent and distributed systems evolves, often resulting in substantial divergence from academic research. In the absence of established tools to express communication protocols, widely used implementations concentrate solely on scalability and reliability. The flip side is that these systems are either overly loose, supporting any conceivable communication structure (via brokers), or overly restricted, supporting only simple request-response protocols (like HTTP or RPC). In this seminar, experts from academia and industry explored together how best to bridge the gap between theory and mainstream practice. They tackled challenges that are fundamental in practical systems development, but are rarely or only partially addressed in the behavioural types literature - in particular, failure handling, asynchronous communication, and dynamic reconfiguration. Moreover they explored how the tools of behavioural types and programming languages theory (such as linearity, gradual types, and dependent types) can help to address these challenges.

Cite as

Mariangiola Dezani, Roland Kuhn, Sam Lindley, and Alceste Scalas. Behavioural Types: Bridging Theory and Practice (Dagstuhl Seminar 21372). In Dagstuhl Reports, Volume 11, Issue 8, pp. 52-75, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@Article{dezani_et_al:DagRep.11.8.52,
  author =	{Dezani, Mariangiola and Kuhn, Roland and Lindley, Sam and Scalas, Alceste},
  title =	{{Behavioural Types: Bridging Theory and Practice (Dagstuhl Seminar 21372)}},
  pages =	{52--75},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2022},
  volume =	{11},
  number =	{8},
  editor =	{Dezani, Mariangiola and Kuhn, Roland and Lindley, Sam and Scalas, Alceste},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.11.8.52},
  URN =		{urn:nbn:de:0030-drops-157699},
  doi =		{10.4230/DagRep.11.8.52},
  annote =	{Keywords: behavioural types, concurrency, programming languages, session types}
}

Document

DOI: 10.4230/DagRep.11.6.54

Scalable Handling of Effects (Dagstuhl Seminar 21292)

Authors: Danel Ahman, Amal Ahmed, Sam Lindley, and Andreas Rossberg

Published in: Dagstuhl Reports, Volume 11, Issue 6 (2021)

Abstract

Built on solid mathematical foundations, effect handlers offer a uniform and elegant approach to programming with user-defined computational effects. They subsume many widely used programming concepts and abstractions, such as actors, async/await, backtracking, coroutines, generators/iterators, and probabilistic programming. As such, they allow language implementers to target a single implementation of effect handlers, freeing language implementers from having to maintain separate ad hoc implementations of each of the features listed above. Due to their wide applicability, effect handlers are enjoying growing interest in academia and industry. For instance, several effect handler oriented research languages are under active development (such as Eff, Frank, and Koka), as are effect handler libraries for mainstream languages (such as C and Java), effect handlers are seeing increasing use in probabilistic programming tools (such as Uber’s Pyro), and proposals are in the pipeline to include them natively in low-level languages (such as WebAssembly). Effect handlers are also a key part of Multicore OCaml, which incorporates an efficient implementation of them for uniformly expressing user-definable concurrency models in the language. However, enabling effect handlers to scale requires tackling some hard problems, both in theory and in practice. Inspired by experience of developing, programming with, and reasoning about effect handlers in practice, we identify five key problem areas to be addressed at this Dagstuhl Seminar in order to enable effect handlers to scale: Safety, Modularity, Interoperability, Legibility, and Efficiency. In particular, we seek answers to the following questions: - How can we enforce safe interaction between effect handler programs and external resources? - How can we enable modular use of effect handlers for programming in the large? - How can we support interoperable effect handler programs written in different languages? - How can we write legible effect handler programs in a style accessible to mainstream programmers? - How can we generate efficient code from effect handler programs?

Cite as

Danel Ahman, Amal Ahmed, Sam Lindley, and Andreas Rossberg. Scalable Handling of Effects (Dagstuhl Seminar 21292). In Dagstuhl Reports, Volume 11, Issue 6, pp. 54-81, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@Article{ahman_et_al:DagRep.11.6.54,
  author =	{Ahman, Danel and Ahmed, Amal and Lindley, Sam and Rossberg, Andreas},
  title =	{{Scalable Handling of Effects (Dagstuhl Seminar 21292)}},
  pages =	{54--81},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2021},
  volume =	{11},
  number =	{6},
  editor =	{Ahman, Danel and Ahmed, Amal and Lindley, Sam and Rossberg, Andreas},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.11.6.54},
  URN =		{urn:nbn:de:0030-drops-155800},
  doi =		{10.4230/DagRep.11.6.54},
  annote =	{Keywords: continuations, Effect handlers, Wasm}
}

Document

DOI: 10.4230/LIPIcs.CONCUR.2021.36

Separating Sessions Smoothly

Authors: Simon Fowler, Wen Kokke, Ornela Dardha, Sam Lindley, and J. Garrett Morris

Published in: LIPIcs, Volume 203, 32nd International Conference on Concurrency Theory (CONCUR 2021)

Abstract

This paper introduces Hypersequent GV (HGV), a modular and extensible core calculus for functional programming with session types that enjoys deadlock freedom, confluence, and strong normalisation. HGV exploits hyper-environments, which are collections of type environments, to ensure that structural congruence is type preserving. As a consequence we obtain a tight operational correspondence between HGV and HCP, a hypersequent-based process-calculus interpretation of classical linear logic. Our translations from HGV to HCP and vice-versa both preserve and reflect reduction. HGV scales smoothly to support Girard’s Mix rule, a crucial ingredient for channel forwarding and exceptions.

Cite as

Simon Fowler, Wen Kokke, Ornela Dardha, Sam Lindley, and J. Garrett Morris. Separating Sessions Smoothly. In 32nd International Conference on Concurrency Theory (CONCUR 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 203, pp. 36:1-36:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{fowler_et_al:LIPIcs.CONCUR.2021.36,
  author =	{Fowler, Simon and Kokke, Wen and Dardha, Ornela and Lindley, Sam and Morris, J. Garrett},
  title =	{{Separating Sessions Smoothly}},
  booktitle =	{32nd International Conference on Concurrency Theory (CONCUR 2021)},
  pages =	{36:1--36:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-203-7},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{203},
  editor =	{Haddad, Serge and Varacca, Daniele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2021.36},
  URN =		{urn:nbn:de:0030-drops-144138},
  doi =		{10.4230/LIPIcs.CONCUR.2021.36},
  annote =	{Keywords: session types, hypersequents, linear lambda calculus}
}

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