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Documents authored by Escardó, Martín H.

Found 5 Possible Name Variants:

Escardó, Martín H.

Document
DOI: 10.4230/LIPIcs.TYPES.2016.7
Parametricity, Automorphisms of the Universe, and Excluded Middle

Authors: Auke B. Booij, Martín H. Escardó, Peter LeFanu Lumsdaine, and Michael Shulman

Published in: LIPIcs, Volume 97, 22nd International Conference on Types for Proofs and Programs (TYPES 2016)

Abstract
It is known that one can construct non-parametric functions by assuming classical axioms. Our work is a converse to that: we prove classical axioms in dependent type theory assuming specific instances of non-parametricity. We also address the interaction between classical axioms and the existence of automorphisms of a type universe. We work over intensional Martin-Löf dependent type theory, and for some results assume further principles including function extensionality, propositional extensionality, propositional truncation, and the univalence axiom.
Cite as

Auke B. Booij, Martín H. Escardó, Peter LeFanu Lumsdaine, and Michael Shulman. Parametricity, Automorphisms of the Universe, and Excluded Middle. In 22nd International Conference on Types for Proofs and Programs (TYPES 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 97, pp. 7:1-7:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{booij_et_al:LIPIcs.TYPES.2016.7,
  author =	{Booij, Auke B. and Escard\'{o}, Mart{\'\i}n H. and Lumsdaine, Peter LeFanu and Shulman, Michael},
  title =	{{Parametricity, Automorphisms of the Universe, and Excluded Middle}},
  booktitle =	{22nd International Conference on Types for Proofs and Programs (TYPES 2016)},
  pages =	{7:1--7:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-065-1},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{97},
  editor =	{Ghilezan, Silvia and Geuvers, Herman and Ivetic, Jelena},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2016.7},
  URN =		{urn:nbn:de:0030-drops-98554},
  doi =		{10.4230/LIPIcs.TYPES.2016.7},
  annote =	{Keywords: relational parametricity, dependent type theory, univalent foundations, homotopy type theory, excluded middle, classical mathematics, constructive mat}
}
Document
DOI: 10.4230/LIPIcs.CSL.2017.21
Partial Elements and Recursion via Dominances in Univalent Type Theory

Authors: Martín H. Escardó and Cory M. Knapp

Published in: LIPIcs, Volume 82, 26th EACSL Annual Conference on Computer Science Logic (CSL 2017)

Abstract
We begin by revisiting partiality in univalent type theory via the notion of dominance. We then perform first steps in constructive computability theory, discussing the consequences of working with computability as property or structure, without assuming countable choice or Markov’s principle. A guiding question is what, if any, notion of partial function allows the proposition “all partial functions on natural numbers are Turing computable” to be consistent.
Cite as

Martín H. Escardó and Cory M. Knapp. Partial Elements and Recursion via Dominances in Univalent Type Theory. In 26th EACSL Annual Conference on Computer Science Logic (CSL 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 82, pp. 21:1-21:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{escardo_et_al:LIPIcs.CSL.2017.21,
  author =	{Escard\'{o}, Mart{\'\i}n H. and Knapp, Cory M.},
  title =	{{Partial Elements and Recursion via Dominances in Univalent Type Theory}},
  booktitle =	{26th EACSL Annual Conference on Computer Science Logic (CSL 2017)},
  pages =	{21:1--21:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-045-3},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{82},
  editor =	{Goranko, Valentin and Dam, Mads},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2017.21},
  URN =		{urn:nbn:de:0030-drops-76822},
  doi =		{10.4230/LIPIcs.CSL.2017.21},
  annote =	{Keywords: univalent type theory, homotopy type theory, partial function, dominance, recursion theory, computability theory}
}

Escardó, Martín

Document
DOI: 10.4230/LIPIcs.TYPES.2022.13
Type Theory with Explicit Universe Polymorphism

Authors: Marc Bezem, Thierry Coquand, Peter Dybjer, and Martín Escardó

Published in: LIPIcs, Volume 269, 28th International Conference on Types for Proofs and Programs (TYPES 2022)

Abstract
The aim of this paper is to refine and extend proposals by Sozeau and Tabareau and by Voevodsky for universe polymorphism in type theory. In those systems judgments can depend on explicit constraints between universe levels. We here present a system where we also have products indexed by universe levels and by constraints. Our theory has judgments for internal universe levels, built up from level variables by a successor operation and a binary supremum operation, and also judgments for equality of universe levels.
Cite as

Marc Bezem, Thierry Coquand, Peter Dybjer, and Martín Escardó. Type Theory with Explicit Universe Polymorphism. In 28th International Conference on Types for Proofs and Programs (TYPES 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 269, pp. 13:1-13:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{bezem_et_al:LIPIcs.TYPES.2022.13,
  author =	{Bezem, Marc and Coquand, Thierry and Dybjer, Peter and Escard\'{o}, Mart{\'\i}n},
  title =	{{Type Theory with Explicit Universe Polymorphism}},
  booktitle =	{28th International Conference on Types for Proofs and Programs (TYPES 2022)},
  pages =	{13:1--13:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-285-3},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{269},
  editor =	{Kesner, Delia and P\'{e}drot, Pierre-Marie},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2022.13},
  URN =		{urn:nbn:de:0030-drops-184564},
  doi =		{10.4230/LIPIcs.TYPES.2022.13},
  annote =	{Keywords: type theory, universes in type theory, universe polymorphism, level-indexed products, constraint-indexed products}
}
Document
DOI: 10.4230/DagRep.8.8.130
Formalization of Mathematics in Type Theory (Dagstuhl Seminar 18341)

Authors: Andrej Bauer, Martín Escardó, Peter L. Lumsdaine, and Assia Mahboubi

Published in: Dagstuhl Reports, Volume 8, Issue 8 (2019)

Abstract
Formalized mathematics is mathematical knowledge (definitions, theorems, and proofs) represented in digital form suitable for computer processing. The central goal of this seminar was to identify the theoretical advances and practical improvements needed in the area of formalized mathematics, in order to make it a mature technology, truly useful to a larger community of students and researchers in mathematics. During the seminar, various software systems for formalization were compared, and potential improvements to existing systems were investigated. There have also been discussions on the representation of algebraic structures in formalization systems.
Cite as

Andrej Bauer, Martín Escardó, Peter L. Lumsdaine, and Assia Mahboubi. Formalization of Mathematics in Type Theory (Dagstuhl Seminar 18341). In Dagstuhl Reports, Volume 8, Issue 8, pp. 130-145, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@Article{bauer_et_al:DagRep.8.8.130,
  author =	{Bauer, Andrej and Escard\'{o}, Mart{\'\i}n and Lumsdaine, Peter L. and Mahboubi, Assia},
  title =	{{Formalization of Mathematics in Type Theory (Dagstuhl Seminar 18341)}},
  pages =	{130--145},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2019},
  volume =	{8},
  number =	{8},
  editor =	{Bauer, Andrej and Escard\'{o}, Mart{\'\i}n and Lumsdaine, Peter L. and Mahboubi, Assia},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.8.8.130},
  URN =		{urn:nbn:de:0030-drops-102370},
  doi =		{10.4230/DagRep.8.8.130},
  annote =	{Keywords: formal methods, formalized mathematics, proof assistant, type theory}
}
Document
DOI: 10.4230/LIPIcs.CSL.2011.233
System T and the Product of Selection Functions

Authors: Martin Escardo, Paulo Oliva, and Thomas Powell

Published in: LIPIcs, Volume 12, Computer Science Logic (CSL'11) - 25th International Workshop/20th Annual Conference of the EACSL (2011)

Abstract
We show that the finite product of selection functions (for all finite types) is primitive recursively equivalent to Goedel's higher-type recursor (for all finite types). The correspondence is shown to hold for similar restricted fragments of both systems: The recursor for type level n+1 is primitive recursively equivalent to the finite product of selection functions of type level n. Whereas the recursor directly interprets induction, we show that other classical arithmetical principles such as bounded collection and finite choice are more naturally interpreted via the product of selection functions.
Cite as

Martin Escardo, Paulo Oliva, and Thomas Powell. System T and the Product of Selection Functions. In Computer Science Logic (CSL'11) - 25th International Workshop/20th Annual Conference of the EACSL. Leibniz International Proceedings in Informatics (LIPIcs), Volume 12, pp. 233-247, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2011)

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@InProceedings{escardo_et_al:LIPIcs.CSL.2011.233,
  author =	{Escardo, Martin and Oliva, Paulo and Powell, Thomas},
  title =	{{System T and the Product of Selection Functions}},
  booktitle =	{Computer Science Logic (CSL'11) - 25th International Workshop/20th Annual Conference of the EACSL},
  pages =	{233--247},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-32-3},
  ISSN =	{1868-8969},
  year =	{2011},
  volume =	{12},
  editor =	{Bezem, Marc},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2011.233},
  URN =		{urn:nbn:de:0030-drops-32341},
  doi =		{10.4230/LIPIcs.CSL.2011.233},
  annote =	{Keywords: primitive recursion, product of selection functions, finite choice, dialectica interpretation}
}
Document
Tutorial
DOI: 10.4230/OASIcs.CCA.2009.2254
Theory and Practice of Higher-type Computation (Tutorial)

Authors: Martin Escardó

Published in: OASIcs, Volume 11, 6th International Conference on Computability and Complexity in Analysis (CCA'09) (2009)

Abstract
In higher-type computation, established by Kleene and Kreisel in the late 1950's (independently), one works with the data types obtained from the discrete natural numbers by closing under finite products and function spaces. For the theory of higher-type programming languages, it is natural to work with a corresponding hierarchy, or type structure, of domains, identified by Ershov and Scott in the late 1960's (again independently). The Kleene-Kreisel and Ershov-Scott hierarchies account for total and partial computation respectively. In this tutorial I'll explain the theory and practice of higher-type computation and programming languages, and develop old and new applications. From a theoretical point of view, I'll present Kleene-Kreisel spaces and Ershov-Scott domains, and relate the two. Moreover, I'll discuss common generalizations, chiefly QCB spaces and equilogical spaces, which admit further useful closure properties, and their relationship to TTE (Schroeder, Simpson. Scott, Bauer, Weihrauch and many others). I'll also present a natural higher-type model of computation/programming language, namely PCF (Platek, Scott, Plotkin). From a practical point of view, I'll introduce a fragment of the language Haskell as a faithful implementation of PCF. Moreover, I'll develop and run several examples (and prove theorems about them), pertaining to (i) exhaustive search of infinite sets in finite time in particular Ulrich Berger's algorithm and generalizations), and (ii) computation with real numbers (in particular Alex Simpson's integration algorithm and generalizations).
Cite as

Martin Escardó. Theory and Practice of Higher-type Computation (Tutorial). In 6th International Conference on Computability and Complexity in Analysis (CCA'09). Open Access Series in Informatics (OASIcs), Volume 11, p. 21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2009)

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@InProceedings{escardo:OASIcs.CCA.2009.2254,
  author =	{Escard\'{o}, Martin},
  title =	{{Theory and Practice of Higher-type Computation}},
  booktitle =	{6th International Conference on Computability and Complexity in Analysis (CCA'09)},
  pages =	{21--21},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-12-5},
  ISSN =	{2190-6807},
  year =	{2009},
  volume =	{11},
  editor =	{Bauer, Andrej and Hertling, Peter and Ko, Ker-I},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.CCA.2009.2254},
  URN =		{urn:nbn:de:0030-drops-22540},
  doi =		{10.4230/OASIcs.CCA.2009.2254},
  annote =	{Keywords: Higher-type computation, domain theory, Kleene-Kreisel spaces, Ershov-Scott domains, QCB spaces, equilogical spaces, PCF}
}

Escardó, Martin

Document
DOI: 10.4230/LIPIcs.TYPES.2022.13
Type Theory with Explicit Universe Polymorphism

Authors: Marc Bezem, Thierry Coquand, Peter Dybjer, and Martín Escardó

Published in: LIPIcs, Volume 269, 28th International Conference on Types for Proofs and Programs (TYPES 2022)

Abstract
The aim of this paper is to refine and extend proposals by Sozeau and Tabareau and by Voevodsky for universe polymorphism in type theory. In those systems judgments can depend on explicit constraints between universe levels. We here present a system where we also have products indexed by universe levels and by constraints. Our theory has judgments for internal universe levels, built up from level variables by a successor operation and a binary supremum operation, and also judgments for equality of universe levels.
Cite as

Marc Bezem, Thierry Coquand, Peter Dybjer, and Martín Escardó. Type Theory with Explicit Universe Polymorphism. In 28th International Conference on Types for Proofs and Programs (TYPES 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 269, pp. 13:1-13:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{bezem_et_al:LIPIcs.TYPES.2022.13,
  author =	{Bezem, Marc and Coquand, Thierry and Dybjer, Peter and Escard\'{o}, Mart{\'\i}n},
  title =	{{Type Theory with Explicit Universe Polymorphism}},
  booktitle =	{28th International Conference on Types for Proofs and Programs (TYPES 2022)},
  pages =	{13:1--13:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-285-3},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{269},
  editor =	{Kesner, Delia and P\'{e}drot, Pierre-Marie},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2022.13},
  URN =		{urn:nbn:de:0030-drops-184564},
  doi =		{10.4230/LIPIcs.TYPES.2022.13},
  annote =	{Keywords: type theory, universes in type theory, universe polymorphism, level-indexed products, constraint-indexed products}
}
Document
DOI: 10.4230/DagRep.8.8.130
Formalization of Mathematics in Type Theory (Dagstuhl Seminar 18341)

Authors: Andrej Bauer, Martín Escardó, Peter L. Lumsdaine, and Assia Mahboubi

Published in: Dagstuhl Reports, Volume 8, Issue 8 (2019)

Abstract
Formalized mathematics is mathematical knowledge (definitions, theorems, and proofs) represented in digital form suitable for computer processing. The central goal of this seminar was to identify the theoretical advances and practical improvements needed in the area of formalized mathematics, in order to make it a mature technology, truly useful to a larger community of students and researchers in mathematics. During the seminar, various software systems for formalization were compared, and potential improvements to existing systems were investigated. There have also been discussions on the representation of algebraic structures in formalization systems.
Cite as

Andrej Bauer, Martín Escardó, Peter L. Lumsdaine, and Assia Mahboubi. Formalization of Mathematics in Type Theory (Dagstuhl Seminar 18341). In Dagstuhl Reports, Volume 8, Issue 8, pp. 130-145, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@Article{bauer_et_al:DagRep.8.8.130,
  author =	{Bauer, Andrej and Escard\'{o}, Mart{\'\i}n and Lumsdaine, Peter L. and Mahboubi, Assia},
  title =	{{Formalization of Mathematics in Type Theory (Dagstuhl Seminar 18341)}},
  pages =	{130--145},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2019},
  volume =	{8},
  number =	{8},
  editor =	{Bauer, Andrej and Escard\'{o}, Mart{\'\i}n and Lumsdaine, Peter L. and Mahboubi, Assia},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.8.8.130},
  URN =		{urn:nbn:de:0030-drops-102370},
  doi =		{10.4230/DagRep.8.8.130},
  annote =	{Keywords: formal methods, formalized mathematics, proof assistant, type theory}
}
Document
DOI: 10.4230/LIPIcs.CSL.2011.233
System T and the Product of Selection Functions

Authors: Martin Escardo, Paulo Oliva, and Thomas Powell

Published in: LIPIcs, Volume 12, Computer Science Logic (CSL'11) - 25th International Workshop/20th Annual Conference of the EACSL (2011)

Abstract
We show that the finite product of selection functions (for all finite types) is primitive recursively equivalent to Goedel's higher-type recursor (for all finite types). The correspondence is shown to hold for similar restricted fragments of both systems: The recursor for type level n+1 is primitive recursively equivalent to the finite product of selection functions of type level n. Whereas the recursor directly interprets induction, we show that other classical arithmetical principles such as bounded collection and finite choice are more naturally interpreted via the product of selection functions.
Cite as

Martin Escardo, Paulo Oliva, and Thomas Powell. System T and the Product of Selection Functions. In Computer Science Logic (CSL'11) - 25th International Workshop/20th Annual Conference of the EACSL. Leibniz International Proceedings in Informatics (LIPIcs), Volume 12, pp. 233-247, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2011)

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@InProceedings{escardo_et_al:LIPIcs.CSL.2011.233,
  author =	{Escardo, Martin and Oliva, Paulo and Powell, Thomas},
  title =	{{System T and the Product of Selection Functions}},
  booktitle =	{Computer Science Logic (CSL'11) - 25th International Workshop/20th Annual Conference of the EACSL},
  pages =	{233--247},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-32-3},
  ISSN =	{1868-8969},
  year =	{2011},
  volume =	{12},
  editor =	{Bezem, Marc},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2011.233},
  URN =		{urn:nbn:de:0030-drops-32341},
  doi =		{10.4230/LIPIcs.CSL.2011.233},
  annote =	{Keywords: primitive recursion, product of selection functions, finite choice, dialectica interpretation}
}
Document
Tutorial
DOI: 10.4230/OASIcs.CCA.2009.2254
Theory and Practice of Higher-type Computation (Tutorial)

Authors: Martin Escardó

Published in: OASIcs, Volume 11, 6th International Conference on Computability and Complexity in Analysis (CCA'09) (2009)

Abstract
In higher-type computation, established by Kleene and Kreisel in the late 1950's (independently), one works with the data types obtained from the discrete natural numbers by closing under finite products and function spaces. For the theory of higher-type programming languages, it is natural to work with a corresponding hierarchy, or type structure, of domains, identified by Ershov and Scott in the late 1960's (again independently). The Kleene-Kreisel and Ershov-Scott hierarchies account for total and partial computation respectively. In this tutorial I'll explain the theory and practice of higher-type computation and programming languages, and develop old and new applications. From a theoretical point of view, I'll present Kleene-Kreisel spaces and Ershov-Scott domains, and relate the two. Moreover, I'll discuss common generalizations, chiefly QCB spaces and equilogical spaces, which admit further useful closure properties, and their relationship to TTE (Schroeder, Simpson. Scott, Bauer, Weihrauch and many others). I'll also present a natural higher-type model of computation/programming language, namely PCF (Platek, Scott, Plotkin). From a practical point of view, I'll introduce a fragment of the language Haskell as a faithful implementation of PCF. Moreover, I'll develop and run several examples (and prove theorems about them), pertaining to (i) exhaustive search of infinite sets in finite time in particular Ulrich Berger's algorithm and generalizations), and (ii) computation with real numbers (in particular Alex Simpson's integration algorithm and generalizations).
Cite as

Martin Escardó. Theory and Practice of Higher-type Computation (Tutorial). In 6th International Conference on Computability and Complexity in Analysis (CCA'09). Open Access Series in Informatics (OASIcs), Volume 11, p. 21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2009)

Copy BibTex To Clipboard

@InProceedings{escardo:OASIcs.CCA.2009.2254,
  author =	{Escard\'{o}, Martin},
  title =	{{Theory and Practice of Higher-type Computation}},
  booktitle =	{6th International Conference on Computability and Complexity in Analysis (CCA'09)},
  pages =	{21--21},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-12-5},
  ISSN =	{2190-6807},
  year =	{2009},
  volume =	{11},
  editor =	{Bauer, Andrej and Hertling, Peter and Ko, Ker-I},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.CCA.2009.2254},
  URN =		{urn:nbn:de:0030-drops-22540},
  doi =		{10.4230/OASIcs.CCA.2009.2254},
  annote =	{Keywords: Higher-type computation, domain theory, Kleene-Kreisel spaces, Ershov-Scott domains, QCB spaces, equilogical spaces, PCF}
}

Escardo, Martin

Document
DOI: 10.4230/LIPIcs.TYPES.2022.13
Type Theory with Explicit Universe Polymorphism

Authors: Marc Bezem, Thierry Coquand, Peter Dybjer, and Martín Escardó

Published in: LIPIcs, Volume 269, 28th International Conference on Types for Proofs and Programs (TYPES 2022)

Abstract
The aim of this paper is to refine and extend proposals by Sozeau and Tabareau and by Voevodsky for universe polymorphism in type theory. In those systems judgments can depend on explicit constraints between universe levels. We here present a system where we also have products indexed by universe levels and by constraints. Our theory has judgments for internal universe levels, built up from level variables by a successor operation and a binary supremum operation, and also judgments for equality of universe levels.
Cite as

Marc Bezem, Thierry Coquand, Peter Dybjer, and Martín Escardó. Type Theory with Explicit Universe Polymorphism. In 28th International Conference on Types for Proofs and Programs (TYPES 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 269, pp. 13:1-13:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{bezem_et_al:LIPIcs.TYPES.2022.13,
  author =	{Bezem, Marc and Coquand, Thierry and Dybjer, Peter and Escard\'{o}, Mart{\'\i}n},
  title =	{{Type Theory with Explicit Universe Polymorphism}},
  booktitle =	{28th International Conference on Types for Proofs and Programs (TYPES 2022)},
  pages =	{13:1--13:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-285-3},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{269},
  editor =	{Kesner, Delia and P\'{e}drot, Pierre-Marie},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2022.13},
  URN =		{urn:nbn:de:0030-drops-184564},
  doi =		{10.4230/LIPIcs.TYPES.2022.13},
  annote =	{Keywords: type theory, universes in type theory, universe polymorphism, level-indexed products, constraint-indexed products}
}
Document
DOI: 10.4230/DagRep.8.8.130
Formalization of Mathematics in Type Theory (Dagstuhl Seminar 18341)

Authors: Andrej Bauer, Martín Escardó, Peter L. Lumsdaine, and Assia Mahboubi

Published in: Dagstuhl Reports, Volume 8, Issue 8 (2019)

Abstract
Formalized mathematics is mathematical knowledge (definitions, theorems, and proofs) represented in digital form suitable for computer processing. The central goal of this seminar was to identify the theoretical advances and practical improvements needed in the area of formalized mathematics, in order to make it a mature technology, truly useful to a larger community of students and researchers in mathematics. During the seminar, various software systems for formalization were compared, and potential improvements to existing systems were investigated. There have also been discussions on the representation of algebraic structures in formalization systems.
Cite as

Andrej Bauer, Martín Escardó, Peter L. Lumsdaine, and Assia Mahboubi. Formalization of Mathematics in Type Theory (Dagstuhl Seminar 18341). In Dagstuhl Reports, Volume 8, Issue 8, pp. 130-145, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@Article{bauer_et_al:DagRep.8.8.130,
  author =	{Bauer, Andrej and Escard\'{o}, Mart{\'\i}n and Lumsdaine, Peter L. and Mahboubi, Assia},
  title =	{{Formalization of Mathematics in Type Theory (Dagstuhl Seminar 18341)}},
  pages =	{130--145},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2019},
  volume =	{8},
  number =	{8},
  editor =	{Bauer, Andrej and Escard\'{o}, Mart{\'\i}n and Lumsdaine, Peter L. and Mahboubi, Assia},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.8.8.130},
  URN =		{urn:nbn:de:0030-drops-102370},
  doi =		{10.4230/DagRep.8.8.130},
  annote =	{Keywords: formal methods, formalized mathematics, proof assistant, type theory}
}
Document
DOI: 10.4230/LIPIcs.CSL.2011.233
System T and the Product of Selection Functions

Authors: Martin Escardo, Paulo Oliva, and Thomas Powell

Published in: LIPIcs, Volume 12, Computer Science Logic (CSL'11) - 25th International Workshop/20th Annual Conference of the EACSL (2011)

Abstract
We show that the finite product of selection functions (for all finite types) is primitive recursively equivalent to Goedel's higher-type recursor (for all finite types). The correspondence is shown to hold for similar restricted fragments of both systems: The recursor for type level n+1 is primitive recursively equivalent to the finite product of selection functions of type level n. Whereas the recursor directly interprets induction, we show that other classical arithmetical principles such as bounded collection and finite choice are more naturally interpreted via the product of selection functions.
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Martin Escardo, Paulo Oliva, and Thomas Powell. System T and the Product of Selection Functions. In Computer Science Logic (CSL'11) - 25th International Workshop/20th Annual Conference of the EACSL. Leibniz International Proceedings in Informatics (LIPIcs), Volume 12, pp. 233-247, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2011)

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@InProceedings{escardo_et_al:LIPIcs.CSL.2011.233,
  author =	{Escardo, Martin and Oliva, Paulo and Powell, Thomas},
  title =	{{System T and the Product of Selection Functions}},
  booktitle =	{Computer Science Logic (CSL'11) - 25th International Workshop/20th Annual Conference of the EACSL},
  pages =	{233--247},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-32-3},
  ISSN =	{1868-8969},
  year =	{2011},
  volume =	{12},
  editor =	{Bezem, Marc},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2011.233},
  URN =		{urn:nbn:de:0030-drops-32341},
  doi =		{10.4230/LIPIcs.CSL.2011.233},
  annote =	{Keywords: primitive recursion, product of selection functions, finite choice, dialectica interpretation}
}
Document
Tutorial
DOI: 10.4230/OASIcs.CCA.2009.2254
Theory and Practice of Higher-type Computation (Tutorial)

Authors: Martin Escardó

Published in: OASIcs, Volume 11, 6th International Conference on Computability and Complexity in Analysis (CCA'09) (2009)

Abstract
In higher-type computation, established by Kleene and Kreisel in the late 1950's (independently), one works with the data types obtained from the discrete natural numbers by closing under finite products and function spaces. For the theory of higher-type programming languages, it is natural to work with a corresponding hierarchy, or type structure, of domains, identified by Ershov and Scott in the late 1960's (again independently). The Kleene-Kreisel and Ershov-Scott hierarchies account for total and partial computation respectively. In this tutorial I'll explain the theory and practice of higher-type computation and programming languages, and develop old and new applications. From a theoretical point of view, I'll present Kleene-Kreisel spaces and Ershov-Scott domains, and relate the two. Moreover, I'll discuss common generalizations, chiefly QCB spaces and equilogical spaces, which admit further useful closure properties, and their relationship to TTE (Schroeder, Simpson. Scott, Bauer, Weihrauch and many others). I'll also present a natural higher-type model of computation/programming language, namely PCF (Platek, Scott, Plotkin). From a practical point of view, I'll introduce a fragment of the language Haskell as a faithful implementation of PCF. Moreover, I'll develop and run several examples (and prove theorems about them), pertaining to (i) exhaustive search of infinite sets in finite time in particular Ulrich Berger's algorithm and generalizations), and (ii) computation with real numbers (in particular Alex Simpson's integration algorithm and generalizations).
Cite as

Martin Escardó. Theory and Practice of Higher-type Computation (Tutorial). In 6th International Conference on Computability and Complexity in Analysis (CCA'09). Open Access Series in Informatics (OASIcs), Volume 11, p. 21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2009)

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@InProceedings{escardo:OASIcs.CCA.2009.2254,
  author =	{Escard\'{o}, Martin},
  title =	{{Theory and Practice of Higher-type Computation}},
  booktitle =	{6th International Conference on Computability and Complexity in Analysis (CCA'09)},
  pages =	{21--21},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-939897-12-5},
  ISSN =	{2190-6807},
  year =	{2009},
  volume =	{11},
  editor =	{Bauer, Andrej and Hertling, Peter and Ko, Ker-I},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.CCA.2009.2254},
  URN =		{urn:nbn:de:0030-drops-22540},
  doi =		{10.4230/OASIcs.CCA.2009.2254},
  annote =	{Keywords: Higher-type computation, domain theory, Kleene-Kreisel spaces, Ershov-Scott domains, QCB spaces, equilogical spaces, PCF}
}

Escardó, Martín Hötzel

Document
DOI: 10.4230/LIPIcs.FSCD.2021.8
Predicative Aspects of Order Theory in Univalent Foundations

Authors: Tom de Jong and Martín Hötzel Escardó

Published in: LIPIcs, Volume 195, 6th International Conference on Formal Structures for Computation and Deduction (FSCD 2021)

Abstract
We investigate predicative aspects of order theory in constructive univalent foundations. By predicative and constructive, we respectively mean that we do not assume Voevodsky’s propositional resizing axioms or excluded middle. Our work complements existing work on predicative mathematics by exploring what cannot be done predicatively in univalent foundations. Our first main result is that nontrivial (directed or bounded) complete posets are necessarily large. That is, if such a nontrivial poset is small, then weak propositional resizing holds. It is possible to derive full propositional resizing if we strengthen nontriviality to positivity. The distinction between nontriviality and positivity is analogous to the distinction between nonemptiness and inhabitedness. We prove our results for a general class of posets, which includes directed complete posets, bounded complete posets and sup-lattices, using a technical notion of a δ_V-complete poset. We also show that nontrivial locally small δ_V-complete posets necessarily lack decidable equality. Specifically, we derive weak excluded middle from assuming a nontrivial locally small δ_V-complete poset with decidable equality. Moreover, if we assume positivity instead of nontriviality, then we can derive full excluded middle. Secondly, we show that each of Zorn’s lemma, Tarski’s greatest fixed point theorem and Pataraia’s lemma implies propositional resizing. Hence, these principles are inherently impredicative and a predicative development of order theory must therefore do without them. Finally, we clarify, in our predicative setting, the relation between the traditional definition of sup-lattice that requires suprema for all subsets and our definition that asks for suprema of all small families.
Cite as

Tom de Jong and Martín Hötzel Escardó. Predicative Aspects of Order Theory in Univalent Foundations. In 6th International Conference on Formal Structures for Computation and Deduction (FSCD 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 195, pp. 8:1-8:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{dejong_et_al:LIPIcs.FSCD.2021.8,
  author =	{de Jong, Tom and Escard\'{o}, Mart{\'\i}n H\"{o}tzel},
  title =	{{Predicative Aspects of Order Theory in Univalent Foundations}},
  booktitle =	{6th International Conference on Formal Structures for Computation and Deduction (FSCD 2021)},
  pages =	{8:1--8:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-191-7},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{195},
  editor =	{Kobayashi, Naoki},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSCD.2021.8},
  URN =		{urn:nbn:de:0030-drops-142461},
  doi =		{10.4230/LIPIcs.FSCD.2021.8},
  annote =	{Keywords: order theory, constructivity, predicativity, univalent foundations}
}
Document
DOI: 10.4230/LIPIcs.CSL.2021.28
Domain Theory in Constructive and Predicative Univalent Foundations

Authors: Tom de Jong and Martín Hötzel Escardó

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

Abstract
We develop domain theory in constructive univalent foundations without Voevodsky’s resizing axioms. In previous work in this direction, we constructed the Scott model of PCF and proved its computational adequacy, based on directed complete posets (dcpos). Here we further consider algebraic and continuous dcpos, and construct Scott’s D_∞ model of the untyped λ-calculus. A common approach to deal with size issues in a predicative foundation is to work with information systems or abstract bases or formal topologies rather than dcpos, and approximable relations rather than Scott continuous functions. Here we instead accept that dcpos may be large and work with type universes to account for this. For instance, in the Scott model of PCF, the dcpos have carriers in the second universe U₁ and suprema of directed families with indexing type in the first universe U₀. Seeing a poset as a category in the usual way, we can say that these dcpos are large, but locally small, and have small filtered colimits. In the case of algebraic dcpos, in order to deal with size issues, we proceed mimicking the definition of accessible category. With such a definition, our construction of Scott’s D_∞ again gives a large, locally small, algebraic dcpo with small directed suprema.
Cite as

Tom de Jong and Martín Hötzel Escardó. Domain Theory in Constructive and Predicative Univalent Foundations. In 29th EACSL Annual Conference on Computer Science Logic (CSL 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 183, pp. 28:1-28:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{dejong_et_al:LIPIcs.CSL.2021.28,
  author =	{de Jong, Tom and Escard\'{o}, Mart{\'\i}n H\"{o}tzel},
  title =	{{Domain Theory in Constructive and Predicative Univalent Foundations}},
  booktitle =	{29th EACSL Annual Conference on Computer Science Logic (CSL 2021)},
  pages =	{28:1--28:18},
  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.2021.28},
  URN =		{urn:nbn:de:0030-drops-134625},
  doi =		{10.4230/LIPIcs.CSL.2021.28},
  annote =	{Keywords: domain theory, constructivity, predicativity, univalent foundations}
}
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