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Invited Talk

**Published in:** LIPIcs, Volume 299, 9th International Conference on Formal Structures for Computation and Deduction (FSCD 2024)

This paper studies the notion of meaningfulness for a unifying framework called dBang-calculus, which subsumes both call-by-name (dCBN) and call-by-value (dCBV). We first define meaningfulness in dBang and then characterize it by means of typability and inhabitation in an associated non-idempotent intersection type system previously appearing in the literature. We validate the proposed notion of meaningfulness by showing two properties: (1) consistency of the smallest theory, called ℋ, equating all meaningless terms, and (2) genericity, stating that meaningless subterms have no bearing on the significance of meaningful terms. The theory ℋ is also shown to have a unique consistent and maximal extension ℋ*, which coincides with a well-known notion of observational equivalence. Last but not least, we show that the notions of meaningfulness and genericity in the literature for dCBN and dCBV are subsumed by the corresponding ones proposed here for the dBang-calculus.

Delia Kesner, Delia Kesner, Victor Arrial, Victor Arrial, Giulio Guerrieri, and Giulio Guerrieri. Meaningfulness and Genericity in a Subsuming Framework (Invited Talk). In 9th International Conference on Formal Structures for Computation and Deduction (FSCD 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 299, pp. 1:1-1:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{kesner_et_al:LIPIcs.FSCD.2024.1, author = {Kesner, Delia and Arrial, Victor and Guerrieri, Giulio}, title = {{Meaningfulness and Genericity in a Subsuming Framework}}, booktitle = {9th International Conference on Formal Structures for Computation and Deduction (FSCD 2024)}, pages = {1:1--1:24}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-323-2}, ISSN = {1868-8969}, year = {2024}, volume = {299}, editor = {Rehof, Jakob}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2024.1}, URN = {urn:nbn:de:0030-drops-203305}, doi = {10.4230/LIPIcs.FSCD.2024.1}, annote = {Keywords: Lambda calculus, Solvability, Meaningfulness, Inhabitation, Genericity} }

Document

**Published in:** LIPIcs, Volume 288, 32nd EACSL Annual Conference on Computer Science Logic (CSL 2024)

We investigate non-wellfounded proof systems based on parsimonious logic, a weaker variant of linear logic where the exponential modality ! is interpreted as a constructor for streams over finite data. Logical consistency is maintained at a global level by adapting a standard progressing criterion. We present an infinitary version of cut-elimination based on finite approximations, and we prove that, in presence of the progressing criterion, it returns well-defined non-wellfounded proofs at its limit. Furthermore, we show that cut-elimination preserves the progressing criterion and various regularity conditions internalizing degrees of proof-theoretical uniformity. Finally, we provide a denotational semantics for our systems based on the relational model.

Matteo Acclavio, Gianluca Curzi, and Giulio Guerrieri. Infinitary Cut-Elimination via Finite Approximations. In 32nd EACSL Annual Conference on Computer Science Logic (CSL 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 288, pp. 8:1-8:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{acclavio_et_al:LIPIcs.CSL.2024.8, author = {Acclavio, Matteo and Curzi, Gianluca and Guerrieri, Giulio}, title = {{Infinitary Cut-Elimination via Finite Approximations}}, booktitle = {32nd EACSL Annual Conference on Computer Science Logic (CSL 2024)}, pages = {8:1--8:19}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-310-2}, ISSN = {1868-8969}, year = {2024}, volume = {288}, editor = {Murano, Aniello 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.CSL.2024.8}, URN = {urn:nbn:de:0030-drops-196510}, doi = {10.4230/LIPIcs.CSL.2024.8}, annote = {Keywords: cut-elimination, non-wellfounded proofs, parsimonious logic, linear logic, proof theory, approximation, sequent calculus, non-uniform proofs} }

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

We present an abstract technique to study normalizing strategies when termination is asymptotic, that is, it appears as a limit. Asymptotic termination occurs in several settings, such as effectful, and in particular probabilistic computation - where the limits are distributions over the possible outputs - or infinitary lambda-calculi - where the limits are infinitary terms such as Böhm trees.
As a concrete application, we obtain a result which is of independent interest: a normalization theorem for Call-by-Value (and - in a uniform way - for Call-by-Name) probabilistic lambda-calculus.

Claudia Faggian and Giulio Guerrieri. Strategies for Asymptotic Normalization. In 7th International Conference on Formal Structures for Computation and Deduction (FSCD 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 228, pp. 17:1-17:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{faggian_et_al:LIPIcs.FSCD.2022.17, author = {Faggian, Claudia and Guerrieri, Giulio}, title = {{Strategies for Asymptotic Normalization}}, booktitle = {7th International Conference on Formal Structures for Computation and Deduction (FSCD 2022)}, pages = {17:1--17:24}, 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.2022.17}, URN = {urn:nbn:de:0030-drops-162987}, doi = {10.4230/LIPIcs.FSCD.2022.17}, annote = {Keywords: rewriting, strategies, normalization, lambda calculus, probabilistic rewriting} }

Document

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

We present a new technique for proving factorization theorems for compound rewriting systems in a modular way, which is inspired by the Hindley-Rosen technique for confluence. Specifically, our approach is well adapted to deal with extensions of the call-by-name and call-by-value λ-calculi.
The technique is first developed abstractly. We isolate a sufficient condition (called linear swap) for lifting factorization from components to the compound system, and which is compatible with β-reduction. We then closely analyze some common factorization schemas for the λ-calculus.
Concretely, we apply our technique to diverse extensions of the λ-calculus, among which de' Liguoro and Piperno’s non-deterministic λ-calculus and - for call-by-value - Carraro and Guerrieri’s shuffling calculus. For both calculi the literature contains factorization theorems. In both cases, we give a new proof which is neat, simpler than the original, and strikingly shorter.

Beniamino Accattoli, Claudia Faggian, and Giulio Guerrieri. Factorize Factorization. In 29th EACSL Annual Conference on Computer Science Logic (CSL 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 183, pp. 6:1-6:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{accattoli_et_al:LIPIcs.CSL.2021.6, author = {Accattoli, Beniamino and Faggian, Claudia and Guerrieri, Giulio}, title = {{Factorize Factorization}}, booktitle = {29th EACSL Annual Conference on Computer Science Logic (CSL 2021)}, pages = {6:1--6:25}, 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.2021.6}, URN = {urn:nbn:de:0030-drops-134407}, doi = {10.4230/LIPIcs.CSL.2021.6}, annote = {Keywords: Lambda Calculus, Rewriting, Reduction Strategies, Factorization} }

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

We investigate intersection types and resource lambda-calculus in deep-inference proof theory. We give a unified type system that is parametric in various aspects: it encompasses resource calculi, intersection-typed lambda-calculus, and simply-typed lambda-calculus; it accommodates both idempotence and non-idempotence; it characterizes strong and weak normalization; and it does so while allowing a range of algebraic laws to determine reduction behaviour, for various quantitative effects. We give a parametric resource calculus with explicit sharing, the "collection calculus", as a Curry-Howard interpretation of the type system, that embodies these computational properties.

Giulio Guerrieri, Willem B. Heijltjes, and Joseph W.N. Paulus. A Deep Quantitative Type System. In 29th EACSL Annual Conference on Computer Science Logic (CSL 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 183, pp. 24:1-24:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{guerrieri_et_al:LIPIcs.CSL.2021.24, author = {Guerrieri, Giulio and Heijltjes, Willem B. and Paulus, Joseph W.N.}, title = {{A Deep Quantitative Type System}}, booktitle = {29th EACSL Annual Conference on Computer Science Logic (CSL 2021)}, pages = {24:1--24:24}, 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.2021.24}, URN = {urn:nbn:de:0030-drops-134586}, doi = {10.4230/LIPIcs.CSL.2021.24}, annote = {Keywords: Lambda-calculus, Deep inference, Intersection types, Resource calculus} }

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

Non-idempotent intersection types can be seen as a syntactic presentation of a well-known denotational semantics for the lambda-calculus, the category of sets and relations. Building on previous work, we present a categorification of this line of thought in the framework of the bang calculus, an untyped version of Levy’s call-by-push-value. We define a bicategorical model for the bang calculus, whose syntactic counterpart is a suitable category of types. In the framework of distributors, we introduce intersection type distributors, a bicategorical proof relevant refinement of relational semantics. Finally, we prove that intersection type distributors characterize normalization at depth 0.

Giulio Guerrieri and Federico Olimpieri. Categorifying Non-Idempotent Intersection Types. In 29th EACSL Annual Conference on Computer Science Logic (CSL 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 183, pp. 25:1-25:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{guerrieri_et_al:LIPIcs.CSL.2021.25, author = {Guerrieri, Giulio and Olimpieri, Federico}, title = {{Categorifying Non-Idempotent Intersection Types}}, booktitle = {29th EACSL Annual Conference on Computer Science Logic (CSL 2021)}, pages = {25:1--25:24}, 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.2021.25}, URN = {urn:nbn:de:0030-drops-134592}, doi = {10.4230/LIPIcs.CSL.2021.25}, annote = {Keywords: Linear logic, bang calculus, non-idempotent intersection types, distributors, relational semantics, combinatorial species, symmetric sequences, bicategory, categorification} }

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**Published in:** LIPIcs, Volume 152, 28th EACSL Annual Conference on Computer Science Logic (CSL 2020)

A Multiplicative-Exponential Linear Logic (MELL) proof-structure can be expanded into a set of resource proof-structures: its Taylor expansion. We introduce a new criterion characterizing those sets of resource proof-structures that are part of the Taylor expansion of some MELL proof-structure, through a rewriting system acting both on resource and MELL proof-structures.

Giulio Guerrieri, Luc Pellissier, and Lorenzo Tortora de Falco. Glueability of Resource Proof-Structures: Inverting the Taylor Expansion. In 28th EACSL Annual Conference on Computer Science Logic (CSL 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 152, pp. 24:1-24:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{guerrieri_et_al:LIPIcs.CSL.2020.24, author = {Guerrieri, Giulio and Pellissier, Luc and Tortora de Falco, Lorenzo}, title = {{Glueability of Resource Proof-Structures: Inverting the Taylor Expansion}}, booktitle = {28th EACSL Annual Conference on Computer Science Logic (CSL 2020)}, pages = {24:1--24:18}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-132-0}, ISSN = {1868-8969}, year = {2020}, volume = {152}, editor = {Fern\'{a}ndez, Maribel and Muscholl, Anca}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2020.24}, URN = {urn:nbn:de:0030-drops-116674}, doi = {10.4230/LIPIcs.CSL.2020.24}, annote = {Keywords: linear logic, Taylor expansion, proof-net, natural transformation} }

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**Published in:** LIPIcs, Volume 52, 1st International Conference on Formal Structures for Computation and Deduction (FSCD 2016)

We show that every connected Multiplicative Exponential Linear Logic (MELL) proof-structure (with or without cuts) is uniquely determined by a well-chosen element of its Taylor expansion: the one obtained by taking two copies of the content of each box. As a consequence, the relational
model is injective with respect to connected MELL proof-structures.

Giulio Guerrieri, Luc Pellissier, and Lorenzo Tortora de Falco. Computing Connected Proof(-Structure)s From Their Taylor Expansion. In 1st International Conference on Formal Structures for Computation and Deduction (FSCD 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 52, pp. 20:1-20:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{guerrieri_et_al:LIPIcs.FSCD.2016.20, author = {Guerrieri, Giulio and Pellissier, Luc and Tortora de Falco, Lorenzo}, title = {{Computing Connected Proof(-Structure)s From Their Taylor Expansion}}, booktitle = {1st International Conference on Formal Structures for Computation and Deduction (FSCD 2016)}, pages = {20:1--20:18}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-010-1}, ISSN = {1868-8969}, year = {2016}, volume = {52}, editor = {Kesner, Delia and Pientka, Brigitte}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2016.20}, URN = {urn:nbn:de:0030-drops-60031}, doi = {10.4230/LIPIcs.FSCD.2016.20}, annote = {Keywords: proof-nets, (differential) linear logic, relational model, Taylor expansion} }

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**Published in:** OASIcs, Volume 46, 2nd International Workshop on Rewriting Techniques for Program Transformations and Evaluation (WPTE 2015)

Recently, a standardization theorem has been proven for a variant of Plotkin's call-by-value lambda-calculus extended by means of two commutation rules (sigma-reductions): this result was based on a partitioning between head and internal reductions. We study the head normalization for this call-by-value calculus with sigma-reductions and we relate it to the weak evaluation of original Plotkin's call-by-value lambda-calculus. We give also a (non-deterministic) normalization strategy for the call-by-value lambda-calculus with sigma-reductions.

Giulio Guerrieri. Head reduction and normalization in a call-by-value lambda-calculus. In 2nd International Workshop on Rewriting Techniques for Program Transformations and Evaluation (WPTE 2015). Open Access Series in Informatics (OASIcs), Volume 46, pp. 3-17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{guerrieri:OASIcs.WPTE.2015.3, author = {Guerrieri, Giulio}, title = {{Head reduction and normalization in a call-by-value lambda-calculus}}, booktitle = {2nd International Workshop on Rewriting Techniques for Program Transformations and Evaluation (WPTE 2015)}, pages = {3--17}, series = {Open Access Series in Informatics (OASIcs)}, ISBN = {978-3-939897-94-1}, ISSN = {2190-6807}, year = {2015}, volume = {46}, editor = {Chiba, Yuki and Escobar, Santiago and Nishida, Naoki and Sabel, David and Schmidt-Schau{\ss}, Manfred}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.WPTE.2015.3}, URN = {urn:nbn:de:0030-drops-51789}, doi = {10.4230/OASIcs.WPTE.2015.3}, annote = {Keywords: sequentialization, lambda-calculus, sigma-reduction, call-by-value, head reduction, internal reduction, (strong) normalization, evaluation, confluence} }

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

We study an extension of Plotkin's call-by-value lambda-calculus by means of two commutation rules (sigma-reductions). Recently, it has been proved that this extended calculus provides elegant characterizations of many semantic properties, as for example solvability. We prove a standardization theorem for this calculus by generalizing Takahashi's approach of parallel reductions. The standardization property allows us to prove that our calculus is conservative with respect to the Plotkin's one. In particular, we show that the notion of solvability for this calculus coincides with that for Plotkin's call-by-value lambda-calculus.

Giulio Guerrieri, Luca Paolini, and Simona Ronchi Della Rocca. Standardization of a Call-By-Value Lambda-Calculus. In 13th International Conference on Typed Lambda Calculi and Applications (TLCA 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 38, pp. 211-225, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{guerrieri_et_al:LIPIcs.TLCA.2015.211, author = {Guerrieri, Giulio and Paolini, Luca and Ronchi Della Rocca, Simona}, title = {{Standardization of a Call-By-Value Lambda-Calculus}}, booktitle = {13th International Conference on Typed Lambda Calculi and Applications (TLCA 2015)}, pages = {211--225}, 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.2015.211}, URN = {urn:nbn:de:0030-drops-51655}, doi = {10.4230/LIPIcs.TLCA.2015.211}, annote = {Keywords: standardization,sequentialization,lambda-calculus,sigma-reduction,par- allel reduction, call-by-value, head reduction, internal reduction, solvability} }

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