DROPS

Volume

LIPIcs, Volume 104

23rd International Conference on Types for Proofs and Programs (TYPES 2017)

TYPES 2017, May 29 to June 1, 2017, Budapest, Hungary

Editors: Andreas Abel, Fredrik Nordvall Forsberg, and Ambrus Kaposi

Document

DOI: 10.4230/LIPIcs.TYPES.2021.10

Quantitative Polynomial Functors

Authors: Georgi Nakov and Fredrik Nordvall Forsberg

Published in: LIPIcs, Volume 239, 27th International Conference on Types for Proofs and Programs (TYPES 2021)

Abstract

We investigate containers and polynomial functors in Quantitative Type Theory, and give initial algebra semantics of inductive data types in the presence of linearity. We show that reasoning by induction is supported, and equivalent to initiality, also in the linear setting.

Cite as

Georgi Nakov and Fredrik Nordvall Forsberg. Quantitative Polynomial Functors. In 27th International Conference on Types for Proofs and Programs (TYPES 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 239, pp. 10:1-10:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{nakov_et_al:LIPIcs.TYPES.2021.10,
  author =	{Nakov, Georgi and Nordvall Forsberg, Fredrik},
  title =	{{Quantitative Polynomial Functors}},
  booktitle =	{27th International Conference on Types for Proofs and Programs (TYPES 2021)},
  pages =	{10:1--10:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-254-9},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{239},
  editor =	{Basold, Henning and Cockx, Jesper and Ghilezan, Silvia},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2021.10},
  URN =		{urn:nbn:de:0030-drops-167795},
  doi =		{10.4230/LIPIcs.TYPES.2021.10},
  annote =	{Keywords: quantitative type theory, polynomial functors, inductive data types}
}

Document

Early Ideas

DOI: 10.4230/LIPIcs.CALCO.2021.22

Quantitative Polynomial Functors (Early Ideas)

Authors: Georgi Nakov and Fredrik Nordvall Forsberg

Published in: LIPIcs, Volume 211, 9th Conference on Algebra and Coalgebra in Computer Science (CALCO 2021)

Abstract

We investigate containers and polynomial functors in Quantitative Type Theory, and give initial algebra semantics of inductive data types in the presence of linearity. We show that reasoning by induction is supported, and equivalent to initiality, also in the linear setting.

Cite as

Georgi Nakov and Fredrik Nordvall Forsberg. Quantitative Polynomial Functors (Early Ideas). In 9th Conference on Algebra and Coalgebra in Computer Science (CALCO 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 211, pp. 22:1-22:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{nakov_et_al:LIPIcs.CALCO.2021.22,
  author =	{Nakov, Georgi and Nordvall Forsberg, Fredrik},
  title =	{{Quantitative Polynomial Functors}},
  booktitle =	{9th Conference on Algebra and Coalgebra in Computer Science (CALCO 2021)},
  pages =	{22:1--22:5},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-212-9},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{211},
  editor =	{Gadducci, Fabio and Silva, Alexandra},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.CALCO.2021.22},
  URN =		{urn:nbn:de:0030-drops-153774},
  doi =		{10.4230/LIPIcs.CALCO.2021.22},
  annote =	{Keywords: quantitative type theory, polynomial functors, inductive data types}
}

Document

DOI: 10.4230/LIPIcs.MFCS.2021.70

Connecting Constructive Notions of Ordinals in Homotopy Type Theory

Authors: Nicolai Kraus, Fredrik Nordvall Forsberg, and Chuangjie Xu

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

Abstract

In classical set theory, there are many equivalent ways to introduce ordinals. In a constructive setting, however, the different notions split apart, with different advantages and disadvantages for each. We consider three different notions of ordinals in homotopy type theory, and show how they relate to each other: A notation system based on Cantor normal forms, a refined notion of Brouwer trees (inductively generated by zero, successor and countable limits), and wellfounded extensional orders. For Cantor normal forms, most properties are decidable, whereas for wellfounded extensional transitive orders, most are undecidable. Formulations for Brouwer trees are usually partially decidable. We demonstrate that all three notions have properties expected of ordinals: their order relations, although defined differently in each case, are all extensional and wellfounded, and the usual arithmetic operations can be defined in each case. We connect these notions by constructing structure preserving embeddings of Cantor normal forms into Brouwer trees, and of these in turn into wellfounded extensional orders. We have formalised most of our results in cubical Agda.

Cite as

Nicolai Kraus, Fredrik Nordvall Forsberg, and Chuangjie Xu. Connecting Constructive Notions of Ordinals in Homotopy Type Theory. In 46th International Symposium on Mathematical Foundations of Computer Science (MFCS 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 202, pp. 70:1-70:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{kraus_et_al:LIPIcs.MFCS.2021.70,
  author =	{Kraus, Nicolai and Nordvall Forsberg, Fredrik and Xu, Chuangjie},
  title =	{{Connecting Constructive Notions of Ordinals in Homotopy Type Theory}},
  booktitle =	{46th International Symposium on Mathematical Foundations of Computer Science (MFCS 2021)},
  pages =	{70:1--70:16},
  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-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2021.70},
  URN =		{urn:nbn:de:0030-drops-145100},
  doi =		{10.4230/LIPIcs.MFCS.2021.70},
  annote =	{Keywords: Constructive ordinals, Cantor normal forms, Brouwer trees}
}

Document

DOI: 10.4230/LIPIcs.TYPES.2019.6

For Finitary Induction-Induction, Induction Is Enough

Authors: Ambrus Kaposi, András Kovács, and Ambroise Lafont

Published in: LIPIcs, Volume 175, 25th International Conference on Types for Proofs and Programs (TYPES 2019)

Abstract

Inductive-inductive types (IITs) are a generalisation of inductive types in type theory. They allow the mutual definition of types with multiple sorts where later sorts can be indexed by previous ones. An example is the Chapman-style syntax of type theory with conversion relations for each sort where e.g. the sort of types is indexed by contexts. In this paper we show that if a model of extensional type theory (ETT) supports indexed W-types, then it supports finitely branching IITs. We use a small internal type theory called the theory of signatures to specify IITs. We show that if a model of ETT supports the syntax for the theory of signatures, then it supports all IITs. We construct this syntax from indexed W-types using preterms and typing relations and prove its initiality following Streicher. The construction of the syntax and its initiality proof were formalised in Agda.

Cite as

Ambrus Kaposi, András Kovács, and Ambroise Lafont. For Finitary Induction-Induction, Induction Is Enough. In 25th International Conference on Types for Proofs and Programs (TYPES 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 175, pp. 6:1-6:30, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{kaposi_et_al:LIPIcs.TYPES.2019.6,
  author =	{Kaposi, Ambrus and Kov\'{a}cs, Andr\'{a}s and Lafont, Ambroise},
  title =	{{For Finitary Induction-Induction, Induction Is Enough}},
  booktitle =	{25th International Conference on Types for Proofs and Programs (TYPES 2019)},
  pages =	{6:1--6:30},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-158-0},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{175},
  editor =	{Bezem, Marc and Mahboubi, Assia},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2019.6},
  URN =		{urn:nbn:de:0030-drops-130707},
  doi =		{10.4230/LIPIcs.TYPES.2019.6},
  annote =	{Keywords: type theory, inductive types, inductive-inductive types}
}

Document

Complete Volume

DOI: 10.4230/LIPIcs.TYPES.2017

LIPIcs, Volume 104, TYPES'17, Complete Volume

Authors: Andreas Abel, Fredrik Nordvall Forsberg, and Ambrus Kaposi

Published in: LIPIcs, Volume 104, 23rd International Conference on Types for Proofs and Programs (TYPES 2017)

Abstract

LIPIcs, Volume 104, TYPES'17, Complete Volume

Cite as

23rd International Conference on Types for Proofs and Programs (TYPES 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 104, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@Proceedings{abel_et_al:LIPIcs.TYPES.2017,
  title =	{{LIPIcs, Volume 104, TYPES'17, Complete Volume}},
  booktitle =	{23rd International Conference on Types for Proofs and Programs (TYPES 2017)},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-071-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{104},
  editor =	{Abel, Andreas and Nordvall Forsberg, Fredrik and Kaposi, Ambrus},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2017},
  URN =		{urn:nbn:de:0030-drops-101671},
  doi =		{10.4230/LIPIcs.TYPES.2017},
  annote =	{Keywords: Theory of computation, Type theory, Proof theory, Program verification}
}

Document

Front Matter

DOI: 10.4230/LIPIcs.TYPES.2017.0

Front Matter, Table of Contents, Preface, Conference Organization

Authors: Andreas Abel, Fredrik Nordvall Forsberg, and Ambrus Kaposi

Published in: LIPIcs, Volume 104, 23rd International Conference on Types for Proofs and Programs (TYPES 2017)

Abstract

Front Matter, Table of Contents, Preface, Conference Organization

Cite as

23rd International Conference on Types for Proofs and Programs (TYPES 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 104, pp. 0:i-0:x, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{abel_et_al:LIPIcs.TYPES.2017.0,
  author =	{Abel, Andreas and Nordvall Forsberg, Fredrik and Kaposi, Ambrus},
  title =	{{Front Matter, Table of Contents, Preface, Conference Organization}},
  booktitle =	{23rd International Conference on Types for Proofs and Programs (TYPES 2017)},
  pages =	{0:i--0:x},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-071-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{104},
  editor =	{Abel, Andreas and Nordvall Forsberg, Fredrik and Kaposi, Ambrus},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2017.0},
  URN =		{urn:nbn:de:0030-drops-100488},
  doi =		{10.4230/LIPIcs.TYPES.2017.0},
  annote =	{Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}

Document

DOI: 10.4230/LIPIcs.TYPES.2017.1

Typing with Leftovers - A mechanization of Intuitionistic Multiplicative-Additive Linear Logic

Authors: Guillaume Allais

Published in: LIPIcs, Volume 104, 23rd International Conference on Types for Proofs and Programs (TYPES 2017)

Abstract

We start from an untyped, well-scoped lambda-calculus and introduce a bidirectional typing relation corresponding to a Multiplicative-Additive Intuitionistic Linear Logic. We depart from typical presentations to adopt one that is well-suited to the intensional setting of Martin-Löf Type Theory. This relation is based on the idea that a linear term consumes some of the resources available in its context whilst leaving behind leftovers which can then be fed to another program. Concretely, this means that typing derivations have both an input and an output context. This leads to a notion of weakening (the extra resources added to the input context come out unchanged in the output one), a rather direct proof of stability under substitution, an analogue of the frame rule of separation logic showing that the state of unused resources can be safely ignored, and a proof that typechecking is decidable. Finally, we demonstrate that this alternative formalization is sound and complete with respect to a more traditional representation of Intuitionistic Linear Logic. The work has been fully formalised in Agda, commented source files are provided as additional material available at https://github.com/gallais/typing-with-leftovers.

Cite as

Guillaume Allais. Typing with Leftovers - A mechanization of Intuitionistic Multiplicative-Additive Linear Logic. In 23rd International Conference on Types for Proofs and Programs (TYPES 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 104, pp. 1:1-1:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{allais:LIPIcs.TYPES.2017.1,
  author =	{Allais, Guillaume},
  title =	{{Typing with Leftovers - A mechanization of Intuitionistic Multiplicative-Additive Linear Logic}},
  booktitle =	{23rd International Conference on Types for Proofs and Programs (TYPES 2017)},
  pages =	{1:1--1:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-071-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{104},
  editor =	{Abel, Andreas and Nordvall Forsberg, Fredrik and Kaposi, Ambrus},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2017.1},
  URN =		{urn:nbn:de:0030-drops-100490},
  doi =		{10.4230/LIPIcs.TYPES.2017.1},
  annote =	{Keywords: Type System, Bidirectional, Linear Logic, Agda}
}

Document

DOI: 10.4230/LIPIcs.TYPES.2017.2

Lower End of the Linial-Post Spectrum

Authors: Andrej Dudenhefner and Jakob Rehof

Published in: LIPIcs, Volume 104, 23rd International Conference on Types for Proofs and Programs (TYPES 2017)

Abstract

We show that recognizing axiomatizations of the Hilbert-style calculus containing only the axiom a -> (b -> a) is undecidable (a reduction from the Post correspondence problem is formalized in the Lean theorem prover). Interestingly, the problem remains undecidable considering only axioms which, when seen as simple types, are principal for some lambda-terms in beta-normal form. This problem is closely related to type-based composition synthesis, i.e. finding a composition of given building blocks (typed terms) satisfying a desired specification (goal type). Contrary to the above result, axiomatizations of the Hilbert-style calculus containing only the axiom a -> (b -> b) are recognizable in linear time.

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Andrej Dudenhefner and Jakob Rehof. Lower End of the Linial-Post Spectrum. In 23rd International Conference on Types for Proofs and Programs (TYPES 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 104, pp. 2:1-2:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{dudenhefner_et_al:LIPIcs.TYPES.2017.2,
  author =	{Dudenhefner, Andrej and Rehof, Jakob},
  title =	{{Lower End of the Linial-Post Spectrum}},
  booktitle =	{23rd International Conference on Types for Proofs and Programs (TYPES 2017)},
  pages =	{2:1--2:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-071-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{104},
  editor =	{Abel, Andreas and Nordvall Forsberg, Fredrik and Kaposi, Ambrus},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2017.2},
  URN =		{urn:nbn:de:0030-drops-100503},
  doi =		{10.4230/LIPIcs.TYPES.2017.2},
  annote =	{Keywords: combinatory logic, lambda calculus, type theory, simple types, inhabitation, principal type}
}

Document

DOI: 10.4230/LIPIcs.TYPES.2017.3

Proof Terms for Generalized Natural Deduction

Authors: Herman Geuvers and Tonny Hurkens

Published in: LIPIcs, Volume 104, 23rd International Conference on Types for Proofs and Programs (TYPES 2017)

Abstract

In previous work it has been shown how to generate natural deduction rules for propositional connectives from truth tables, both for classical and constructive logic. The present paper extends this for the constructive case with proof-terms, thereby extending the Curry-Howard isomorphism to these new connectives. A general notion of conversion of proofs is defined, both as a conversion of derivations and as a reduction of proof-terms. It is shown how the well-known rules for natural deduction (Gentzen, Prawitz) and general elimination rules (Schroeder-Heister, von Plato, and others), and their proof conversions can be found as instances. As an illustration of the power of the method, we give constructive rules for the nand logical operator (also called Sheffer stroke). As usual, conversions come in two flavours: either a detour conversion arising from a detour convertibility, where an introduction rule is immediately followed by an elimination rule, or a permutation conversion arising from an permutation convertibility, an elimination rule nested inside another elimination rule. In this paper, both are defined for the general setting, as conversions of derivations and as reductions of proof-terms. The properties of these are studied as proof-term reductions. As one of the main contributions it is proved that detour conversion is strongly normalizing and permutation conversion is strongly normalizing: no matter how one reduces, the process eventually terminates. Furthermore, the combination of the two conversions is shown to be weakly normalizing: one can always reduce away all convertibilities.

Cite as

Herman Geuvers and Tonny Hurkens. Proof Terms for Generalized Natural Deduction. In 23rd International Conference on Types for Proofs and Programs (TYPES 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 104, pp. 3:1-3:39, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{geuvers_et_al:LIPIcs.TYPES.2017.3,
  author =	{Geuvers, Herman and Hurkens, Tonny},
  title =	{{Proof Terms for Generalized Natural Deduction}},
  booktitle =	{23rd International Conference on Types for Proofs and Programs (TYPES 2017)},
  pages =	{3:1--3:39},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-071-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{104},
  editor =	{Abel, Andreas and Nordvall Forsberg, Fredrik and Kaposi, Ambrus},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2017.3},
  URN =		{urn:nbn:de:0030-drops-100519},
  doi =		{10.4230/LIPIcs.TYPES.2017.3},
  annote =	{Keywords: constructive logic, natural deduction, detour conversion, permutation conversion, normalization Curry-Howard isomorphism}
}

Document

DOI: 10.4230/LIPIcs.TYPES.2017.4

PML2: Integrated Program Verification in ML

Authors: Rodolphe Lepigre

Published in: LIPIcs, Volume 104, 23rd International Conference on Types for Proofs and Programs (TYPES 2017)

Abstract

We present the PML_2 language, which provides a uniform environment for programming, and for proving properties of programs in an ML-like setting. The language is Curry-style and call-by-value, it provides a control operator (interpreted in terms of classical logic), it supports general recursion and a very general form of (implicit, non-coercive) subtyping. In the system, equational properties of programs are expressed using two new type formers, and they are proved by constructing terminating programs. Although proofs rely heavily on equational reasoning, equalities are exclusively managed by the type-checker. This means that the user only has to choose which equality to use, and not where to use it, as is usually done in mathematical proofs. In the system, writing proofs mostly amounts to applying lemmas (possibly recursive function calls), and to perform case analyses (pattern matchings).

Cite as

Rodolphe Lepigre. PML2: Integrated Program Verification in ML. In 23rd International Conference on Types for Proofs and Programs (TYPES 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 104, pp. 4:1-4:27, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{lepigre:LIPIcs.TYPES.2017.4,
  author =	{Lepigre, Rodolphe},
  title =	{{PML2: Integrated Program Verification in ML}},
  booktitle =	{23rd International Conference on Types for Proofs and Programs (TYPES 2017)},
  pages =	{4:1--4:27},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-071-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{104},
  editor =	{Abel, Andreas and Nordvall Forsberg, Fredrik and Kaposi, Ambrus},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2017.4},
  URN =		{urn:nbn:de:0030-drops-100521},
  doi =		{10.4230/LIPIcs.TYPES.2017.4},
  annote =	{Keywords: program verification, classical logic, ML-like language, termination checking, Curry-style quantification, implicit subtyping}
}

Document

DOI: 10.4230/LIPIcs.TYPES.2017.5

Formalized Proof Systems for Propositional Logic

Authors: Julius Michaelis and Tobias Nipkow

Published in: LIPIcs, Volume 104, 23rd International Conference on Types for Proofs and Programs (TYPES 2017)

Abstract

We have formalized a range of proof systems for classical propositional logic (sequent calculus, natural deduction, Hilbert systems, resolution) in Isabelle/HOL and have proved the most important meta-theoretic results about semantics and proofs: compactness, soundness, completeness, translations between proof systems, cut-elimination, interpolation and model existence.

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Julius Michaelis and Tobias Nipkow. Formalized Proof Systems for Propositional Logic. In 23rd International Conference on Types for Proofs and Programs (TYPES 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 104, pp. 5:1-5:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{michaelis_et_al:LIPIcs.TYPES.2017.5,
  author =	{Michaelis, Julius and Nipkow, Tobias},
  title =	{{Formalized Proof Systems for Propositional Logic}},
  booktitle =	{23rd International Conference on Types for Proofs and Programs (TYPES 2017)},
  pages =	{5:1--5:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-071-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{104},
  editor =	{Abel, Andreas and Nordvall Forsberg, Fredrik and Kaposi, Ambrus},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2017.5},
  URN =		{urn:nbn:de:0030-drops-100537},
  doi =		{10.4230/LIPIcs.TYPES.2017.5},
  annote =	{Keywords: formalization of logic, proof systems, sequent calculus, natural deduction, resolution}
}

Document

DOI: 10.4230/LIPIcs.TYPES.2017.6

Decomposing the Univalence Axiom

Authors: Ian Orton and Andrew M. Pitts

Published in: LIPIcs, Volume 104, 23rd International Conference on Types for Proofs and Programs (TYPES 2017)

Abstract

This paper investigates Voevodsky's univalence axiom in intensional Martin-Löf type theory. In particular, it looks at how univalence can be derived from simpler axioms. We first present some existing work, collected together from various published and unpublished sources; we then present a new decomposition of the univalence axiom into simpler axioms. We argue that these axioms are easier to verify in certain potential models of univalent type theory, particularly those models based on cubical sets. Finally we show how this decomposition is relevant to an open problem in type theory.

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Ian Orton and Andrew M. Pitts. Decomposing the Univalence Axiom. In 23rd International Conference on Types for Proofs and Programs (TYPES 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 104, pp. 6:1-6:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{orton_et_al:LIPIcs.TYPES.2017.6,
  author =	{Orton, Ian and Pitts, Andrew M.},
  title =	{{Decomposing the Univalence Axiom}},
  booktitle =	{23rd International Conference on Types for Proofs and Programs (TYPES 2017)},
  pages =	{6:1--6:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-071-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{104},
  editor =	{Abel, Andreas and Nordvall Forsberg, Fredrik and Kaposi, Ambrus},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2017.6},
  URN =		{urn:nbn:de:0030-drops-100546},
  doi =		{10.4230/LIPIcs.TYPES.2017.6},
  annote =	{Keywords: dependent type theory, homotopy type theory, univalent type theory, univalence, cubical type theory, cubical sets}
}

Document

DOI: 10.4230/LIPIcs.TYPES.2017.7

On Equality of Objects in Categories in Constructive Type Theory

Authors: Erik Palmgren

Published in: LIPIcs, Volume 104, 23rd International Conference on Types for Proofs and Programs (TYPES 2017)

Abstract

In this note we remark on the problem of equality of objects in categories formalized in Martin-Löf's constructive type theory. A standard notion of category in this system is E-category, where no such equality is specified. The main observation here is that there is no general extension of E-categories to categories with equality on objects, unless the principle Uniqueness of Identity Proofs (UIP) holds. We also introduce the notion of an H-category with equality on objects, which makes it easy to compare to the notion of univalent category proposed for Univalent Type Theory by Ahrens, Kapulkin and Shulman.

Cite as

Erik Palmgren. On Equality of Objects in Categories in Constructive Type Theory. In 23rd International Conference on Types for Proofs and Programs (TYPES 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 104, pp. 7:1-7:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{palmgren:LIPIcs.TYPES.2017.7,
  author =	{Palmgren, Erik},
  title =	{{On Equality of Objects in Categories in Constructive Type Theory}},
  booktitle =	{23rd International Conference on Types for Proofs and Programs (TYPES 2017)},
  pages =	{7:1--7:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-071-2},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{104},
  editor =	{Abel, Andreas and Nordvall Forsberg, Fredrik and Kaposi, Ambrus},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2017.7},
  URN =		{urn:nbn:de:0030-drops-100553},
  doi =		{10.4230/LIPIcs.TYPES.2017.7},
  annote =	{Keywords: type theory, formalization, category theory, setoids}
}

Document

DOI: 10.4230/LIPIcs.MFCS.2017.63

Variations on Inductive-Recursive Definitions

Authors: Neil Ghani, Conor McBride, Fredrik Nordvall Forsberg, and Stephan Spahn

Published in: LIPIcs, Volume 83, 42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017)

Abstract

Dybjer and Setzer introduced the definitional principle of inductive-recursively defined families - i.e. of families (U : Set, T : U -> D) such that the inductive definition of U may depend on the recursively defined T --- by defining a type DS D E of codes. Each c : DS D E defines a functor [c] : Fam D -> Fam E, and (U, T) = \mu [c] : Fam D is exhibited as the initial algebra of [c]. This paper considers the composition of DS-definable functors: Given F : Fam C -> Fam D and G : Fam D -> Fam E, is G \circ F : Fam C -> Fam E DS-definable, if F and G are? We show that this is the case if and only if powers of families are DS-definable, which seems unlikely. To construct composition, we present two new systems UF and PN of codes for inductive-recursive definitions, with UF a subsytem of DS a subsystem of PN. Both UF and PN are closed under composition. Since PN defines a potentially larger class of functors, we show that there is a model where initial algebras of PN-functors exist by adapting Dybjer-Setzer's proof for DS.

Cite as

Neil Ghani, Conor McBride, Fredrik Nordvall Forsberg, and Stephan Spahn. Variations on Inductive-Recursive Definitions. In 42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 83, pp. 63:1-63:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{ghani_et_al:LIPIcs.MFCS.2017.63,
  author =	{Ghani, Neil and McBride, Conor and Nordvall Forsberg, Fredrik and Spahn, Stephan},
  title =	{{Variations on Inductive-Recursive Definitions}},
  booktitle =	{42nd International Symposium on Mathematical Foundations of Computer Science (MFCS 2017)},
  pages =	{63:1--63:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-046-0},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{83},
  editor =	{Larsen, Kim G. and Bodlaender, Hans L. and Raskin, Jean-Francois},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops-dev.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2017.63},
  URN =		{urn:nbn:de:0030-drops-81184},
  doi =		{10.4230/LIPIcs.MFCS.2017.63},
  annote =	{Keywords: Type Theory, induction-recursion, initial-algebra semantics}
}

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