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Documents authored by Tsampas, Stelios

Document
DOI: 10.4230/LIPIcs.CONCUR.2026.38
Compositionality in Coalgebraic Trace Semantics

Authors: Robin Jourde, Henning Urbat, Sergey Goncharov, Stelios Tsampas, and Jonas Forster

Published in: LIPIcs, Volume 391, 37th International Conference on Concurrency Theory (CONCUR 2026)

Abstract
A key requirement on any well-behaved process language is its compositionality: behavioural equivalence of processes should be respected by the constructors of the language. Turi and Plotkin’s abstract GSOS provides an elegant bialgebraic framework for modelling rule formats that guarantee compositionality from the outset. Their original results, however, are restricted to compositionality of strong bisimilarity, a rather fine-grained notion of process equivalence. In the present paper, we demonstrate that Turi and Plotkin’s approach also applies to trace equivalence, which only observes external actions of processes. To this end, we revisit the general compositionality result of their original theory and present it in a refined form with regard to the required naturality conditions. This step makes abstract GSOS applicable over Kleisli categories and thereby enables reasoning about compositionality in the setting of coalgebraic trace semantics. As our main contribution, we introduce De Simone laws, a type of GSOS laws over Kleisli categories, and prove that their operational models are compositional for coalgebraic trace equivalence. This result recovers and explains compositionality of the well-known De Simone rule format for labelled transition systems in a natural categorical setting. As a further application, we derive from our general framework a novel De Simone-type format for probabilistic systems, compositional for probabilistic trace equivalence.
Cite as

Robin Jourde, Henning Urbat, Sergey Goncharov, Stelios Tsampas, and Jonas Forster. Compositionality in Coalgebraic Trace Semantics. In 37th International Conference on Concurrency Theory (CONCUR 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 391, pp. 38:1-38:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{jourde_et_al:LIPIcs.CONCUR.2026.38,
  author =	{Jourde, Robin and Urbat, Henning and Goncharov, Sergey and Tsampas, Stelios and Forster, Jonas},
  title =	{{Compositionality in Coalgebraic Trace Semantics}},
  booktitle =	{37th International Conference on Concurrency Theory (CONCUR 2026)},
  pages =	{38:1--38:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-447-5},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{391},
  editor =	{Sokolova, Ana and Totzke, Patrick},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2026.38},
  URN =		{urn:nbn:de:0030-drops-273680},
  doi =		{10.4230/LIPIcs.CONCUR.2026.38},
  annote =	{Keywords: Coalgebra, Operational Semantics, Process Algebra, Abstract GSOS, Trace Semantics, Rule Formats}
}
Document
Early Ideas
DOI: 10.4230/LIPIcs.CALCO.2023.22
CRDTs, Coalgebraically (Early Ideas)

Authors: Nathan Liittschwager, Stelios Tsampas, Jonathan Castello, and Lindsey Kuper

Published in: LIPIcs, Volume 270, 10th Conference on Algebra and Coalgebra in Computer Science (CALCO 2023)

Abstract
We describe ongoing work that models conflict-free replicated data types (CRDTs) from a coalgebraic point of view. CRDTs are data structures designed for replication across multiple physical locations in a distributed system. We show how to model a CRDT at the local replica level using a novel coalgebraic semantics for CRDTs. We believe this is the first step towards presenting a unified theory for specifying and verifying CRDTs and replicated state machines. As a case study, we consider emulation of CRDTs in terms of coalgebra.
Cite as

Nathan Liittschwager, Stelios Tsampas, Jonathan Castello, and Lindsey Kuper. CRDTs, Coalgebraically (Early Ideas). In 10th Conference on Algebra and Coalgebra in Computer Science (CALCO 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 270, pp. 22:1-22:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{liittschwager_et_al:LIPIcs.CALCO.2023.22,
  author =	{Liittschwager, Nathan and Tsampas, Stelios and Castello, Jonathan and Kuper, Lindsey},
  title =	{{CRDTs, Coalgebraically}},
  booktitle =	{10th Conference on Algebra and Coalgebra in Computer Science (CALCO 2023)},
  pages =	{22:1--22:5},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-287-7},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{270},
  editor =	{Baldan, Paolo and de Paiva, Valeria},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CALCO.2023.22},
  URN =		{urn:nbn:de:0030-drops-188198},
  doi =		{10.4230/LIPIcs.CALCO.2023.22},
  annote =	{Keywords: Coalgebra, Distributed Systems, Concurrency, Bisimulation}
}
Document
Early Ideas
DOI: 10.4230/LIPIcs.CALCO.2023.24
Higher-Order Mathematical Operational Semantics (Early Ideas)

Authors: Sergey Goncharov, Stefan Milius, Lutz Schröder, Stelios Tsampas, and Henning Urbat

Published in: LIPIcs, Volume 270, 10th Conference on Algebra and Coalgebra in Computer Science (CALCO 2023)

Abstract
We present a higher-order extension of Turi and Plotkin’s abstract GSOS framework that retains the key feature of the latter: for every language whose operational rules are represented by a higher-order GSOS law, strong bisimilarity on the canonical operational model is a congruence with respect to the operations of the language. We further extend this result to weak (bi-)similarity, for which a categorical account of Howe’s method is developed. It encompasses, for instance, Abramsky’s classical compositionality theorem for applicative similarity in the untyped λ-calculus. In addition, we give first steps of a theory of logical relations at the level of higher-order abstract GSOS.
Cite as

Sergey Goncharov, Stefan Milius, Lutz Schröder, Stelios Tsampas, and Henning Urbat. Higher-Order Mathematical Operational Semantics (Early Ideas). In 10th Conference on Algebra and Coalgebra in Computer Science (CALCO 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 270, pp. 24:1-24:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{goncharov_et_al:LIPIcs.CALCO.2023.24,
  author =	{Goncharov, Sergey and Milius, Stefan and Schr\"{o}der, Lutz and Tsampas, Stelios and Urbat, Henning},
  title =	{{Higher-Order Mathematical Operational Semantics}},
  booktitle =	{10th Conference on Algebra and Coalgebra in Computer Science (CALCO 2023)},
  pages =	{24:1--24:3},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-287-7},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{270},
  editor =	{Baldan, Paolo and de Paiva, Valeria},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CALCO.2023.24},
  URN =		{urn:nbn:de:0030-drops-188213},
  doi =		{10.4230/LIPIcs.CALCO.2023.24},
  annote =	{Keywords: Abstract GSOS, lambda-calculus, applicative bisimilarity, bialgebra}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2022.30
Stateful Structural Operational Semantics

Authors: Sergey Goncharov, Stefan Milius, Lutz Schröder, Stelios Tsampas, and Henning Urbat

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

Abstract
Compositionality of denotational semantics is an important concern in programming semantics. Mathematical operational semantics in the sense of Turi and Plotkin guarantees compositionality, but seen from the point of view of stateful computation it applies only to very fine-grained equivalences that essentially assume unrestricted interference by the environment between any two statements. We introduce the more restrictive stateful SOS rule format for stateful languages. We show that compositionality of two more coarse-grained semantics, respectively given by assuming read-only interference or no interference between steps, remains an undecidable property even for stateful SOS. However, further restricting the rule format in a manner inspired by the cool GSOS formats of Bloom and van Glabbeek, we obtain the streamlined and cool stateful SOS formats, which respectively guarantee compositionality of the two more abstract equivalences.
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Sergey Goncharov, Stefan Milius, Lutz Schröder, Stelios Tsampas, and Henning Urbat. Stateful Structural Operational Semantics. In 7th International Conference on Formal Structures for Computation and Deduction (FSCD 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 228, pp. 30:1-30:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{goncharov_et_al:LIPIcs.FSCD.2022.30,
  author =	{Goncharov, Sergey and Milius, Stefan and Schr\"{o}der, Lutz and Tsampas, Stelios and Urbat, Henning},
  title =	{{Stateful Structural Operational Semantics}},
  booktitle =	{7th International Conference on Formal Structures for Computation and Deduction (FSCD 2022)},
  pages =	{30:1--30:19},
  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.2022.30},
  URN =		{urn:nbn:de:0030-drops-163111},
  doi =		{10.4230/LIPIcs.FSCD.2022.30},
  annote =	{Keywords: Structural Operational Semantics, Rule Formats, Distributive Laws}
}
Document
DOI: 10.4230/LIPIcs.MFCS.2021.88
Abstract Congruence Criteria for Weak Bisimilarity

Authors: Stelios Tsampas, Christian Williams, Andreas Nuyts, Dominique Devriese, and Frank Piessens

Published in: LIPIcs, Volume 202, 46th International Symposium on Mathematical Foundations of Computer Science (MFCS 2021)

Abstract
We introduce three general compositionality criteria over operational semantics and prove that, when all three are satisfied together, they guarantee weak bisimulation being a congruence. Our work is founded upon Turi and Plotkin’s mathematical operational semantics and the coalgebraic approach to weak bisimulation by Brengos. We demonstrate each criterion with various examples of success and failure and establish a formal connection with the simply WB cool rule format of Bloom and van Glabbeek. In addition, we show that the three criteria induce lax models in the sense of Bonchi et al.
Cite as

Stelios Tsampas, Christian Williams, Andreas Nuyts, Dominique Devriese, and Frank Piessens. Abstract Congruence Criteria for Weak Bisimilarity. In 46th International Symposium on Mathematical Foundations of Computer Science (MFCS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 202, pp. 88:1-88:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{tsampas_et_al:LIPIcs.MFCS.2021.88,
  author =	{Tsampas, Stelios and Williams, Christian and Nuyts, Andreas and Devriese, Dominique and Piessens, Frank},
  title =	{{Abstract Congruence Criteria for Weak Bisimilarity}},
  booktitle =	{46th International Symposium on Mathematical Foundations of Computer Science (MFCS 2021)},
  pages =	{88:1--88:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-201-3},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{202},
  editor =	{Bonchi, Filippo and Puglisi, Simon J.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2021.88},
  URN =		{urn:nbn:de:0030-drops-145281},
  doi =		{10.4230/LIPIcs.MFCS.2021.88},
  annote =	{Keywords: Structural Operational Semantics, distributive laws, weak bisimilarity}
}

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