Search Results

Documents authored by Mörtberg, Anders

Artifact
Software
DOI: 10.4230/artifacts.26876
A Computer Formalisation of the Serre Finiteness Theorem (accompanying formalisation)

Authors: Reid Barton, Axel Ljungström, Owen Milner, and Anders Mörtberg

Abstract
Cite as

Reid Barton, Axel Ljungström, Owen Milner, Anders Mörtberg. A Computer Formalisation of the Serre Finiteness Theorem (accompanying formalisation) (Software). Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

Copy BibTex To Clipboard

@misc{SerreFiniteness,
   title = {{A Computer Formalisation of the Serre Finiteness Theorem (accompanying formalisation)}}, 
   author = {Barton, Reid and Ljungstr\"{o}m, Axel and Milner, Owen and M\"{o}rtberg, Anders},
   note = {Software, ForCUTT project, ERC advanced grant 101053291, Knut & Alice Wallenberg Foundation’s Program for Mathematics, This material is based upon work supported by the Air Force Office of Scientific Research under award number FA9550-21-1-0009, PI Steve Awodey, swhId: \href{https://archive.softwareheritage.org/swh:1:dir:5c9314da89014673a22878132bb63cfc42ccfa73;origin=https://github.com/CMU-HoTT/serre-finiteness;visit=swh:1:snp:0f3bfe0f67361dc33562f0fc15b80309b3290611;anchor=swh:1:rev:79f3150942a129eb544004adcdef4b17244d5ed4}{\texttt{swh:1:dir:5c9314da89014673a22878132bb63cfc42ccfa73}} (visited on 2026-07-09)},
   url = {https://github.com/CMU-HoTT/serre-finiteness},
   doi = {10.4230/artifacts.26876},
}
Document
DOI: 10.4230/LIPIcs.LICS.2026.16
A Computer Formalisation of the Serre Finiteness Theorem

Authors: Reid Barton, Axel Ljungström, Owen Milner, and Anders Mörtberg

Published in: LIPIcs, Volume 380, 41st Annual Symposium on Logic in Computer Science (LICS 2026)

Abstract
Few constructions in mathematics are as elusive as the homotopy groups of spheres. These groups, which intuitively measure n-dimensional loops on m-dimensional spheres, appear at first glance to be almost completely random - an unfortunate fact, seeing as they constitute one of the fundamental building blocks of algebraic topology and homotopy theory. However, the situation is not completely hopeless: in 1951, Serre proved his celebrated finiteness theorem, which says that these groups are almost always finite abelian groups, except in two classes of special cases when they also contain copies of the integers. In a recent paper, Barton and Campion proved a variation of this result in homotopy type theory (HoTT) - an extension of Martin-Löf type theory, particularly suitable for reasoning about and formalising algebraic topology and homotopy theory. Their result shows that the homotopy groups of spheres are all finitely presented - and constructively so. Prior to this proof, only low-dimensional homotopy groups of spheres had been computed in HoTT. This made it a major breakthrough for HoTT as a foundation and, as such, the immediate target of a full-scale formalisation project. In this paper, we present the outcome of this project: a complete formalisation of Barton and Campion’s proof of the Serre finiteness theorem in Cubical Agda, a constructive proof assistant implementing a cubical flavour of HoTT. In the light of the constructivity of Cubical Agda, we discuss the prospect of running the algorithm provided by our formalisation in order to compute concrete homotopy groups of spheres.
Cite as

Reid Barton, Axel Ljungström, Owen Milner, and Anders Mörtberg. A Computer Formalisation of the Serre Finiteness Theorem. In 41st Annual Symposium on Logic in Computer Science (LICS 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 380, pp. 16:1-16:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

Copy BibTex To Clipboard

@InProceedings{barton_et_al:LIPIcs.LICS.2026.16,
  author =	{Barton, Reid and Ljungstr\"{o}m, Axel and Milner, Owen and M\"{o}rtberg, Anders},
  title =	{{A Computer Formalisation of the Serre Finiteness Theorem}},
  booktitle =	{41st Annual Symposium on Logic in Computer Science (LICS 2026)},
  pages =	{16:1--16:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-434-5},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{380},
  editor =	{Faggian, Claudia and Katoen, Joost-Pieter},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.LICS.2026.16},
  URN =		{urn:nbn:de:0030-drops-268031},
  doi =		{10.4230/LIPIcs.LICS.2026.16},
  annote =	{Keywords: Homotopy type theory, synthetic homotopy theory, formalisation of mathematics, constructive mathematics}
}
Document
DOI: 10.4230/LIPIcs.FSCD.2024.22
Automating Boundary Filling in Cubical Agda

Authors: Maximilian Doré, Evan Cavallo, and Anders Mörtberg

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

Abstract
When working in a proof assistant, automation is key to discharging routine proof goals such as equations between algebraic expressions. Homotopy Type Theory allows the user to reason about higher structures, such as topological spaces, using higher inductive types (HITs) and univalence. Cubical Agda is an extension of Agda with computational support for HITs and univalence. A difficulty when working in Cubical Agda is dealing with the complex combinatorics of higher structures, an infinite-dimensional generalisation of equational reasoning. To solve these higher-dimensional equations consists in constructing cubes with specified boundaries. We develop a simplified cubical language in which we isolate and study two automation problems: contortion solving, where we attempt to "contort" a cube to fit a given boundary, and the more general Kan solving, where we search for solutions that involve pasting multiple cubes together. Both problems are difficult in the general case - Kan solving is even undecidable - so we focus on heuristics that perform well on practical examples. We provide a solver for the contortion problem using a reformulation of contortions in terms of poset maps, while we solve Kan problems using constraint satisfaction programming. We have implemented our algorithms in an experimental Haskell solver that can be used to automatically solve goals presented by Cubical Agda. We illustrate this with a case study establishing the Eckmann-Hilton theorem using our solver, as well as various benchmarks - providing the ground for further study of proof automation in cubical type theories.
Cite as

Maximilian Doré, Evan Cavallo, and Anders Mörtberg. Automating Boundary Filling in Cubical Agda. In 9th International Conference on Formal Structures for Computation and Deduction (FSCD 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 299, pp. 22:1-22:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

Copy BibTex To Clipboard

@InProceedings{dore_et_al:LIPIcs.FSCD.2024.22,
  author =	{Dor\'{e}, Maximilian and Cavallo, Evan and M\"{o}rtberg, Anders},
  title =	{{Automating Boundary Filling in Cubical Agda}},
  booktitle =	{9th International Conference on Formal Structures for Computation and Deduction (FSCD 2024)},
  pages =	{22:1--22:18},
  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.2024.22},
  URN =		{urn:nbn:de:0030-drops-203514},
  doi =		{10.4230/LIPIcs.FSCD.2024.22},
  annote =	{Keywords: Cubical Agda, Automated Reasoning, Constraint Satisfaction Programming}
}
Document
DOI: 10.4230/LIPIcs.TYPES.2022.14
A Univalent Formalization of Constructive Affine Schemes

Authors: Max Zeuner and Anders Mörtberg

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

Abstract
We present a formalization of constructive affine schemes in the Cubical Agda proof assistant. This development is not only fully constructive and predicative, it also makes crucial use of univalence. By now schemes have been formalized in various proof assistants. However, most existing formalizations follow the inherently non-constructive approach of Hartshorne’s classic "Algebraic Geometry" textbook, for which the construction of the so-called structure sheaf is rather straightforwardly formalizable and works the same with or without univalence. We follow an alternative approach that uses a point-free description of the constructive counterpart of the Zariski spectrum called the Zariski lattice and proceeds by defining the structure sheaf on formal basic opens and then lift it to the whole lattice. This general strategy is used in a plethora of textbooks, but formalizing it has proved tricky. The main result of this paper is that with the help of the univalence principle we can make this "lift from basis" strategy formal and obtain a fully formalized account of constructive affine schemes.
Cite as

Max Zeuner and Anders Mörtberg. A Univalent Formalization of Constructive Affine Schemes. In 28th International Conference on Types for Proofs and Programs (TYPES 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 269, pp. 14:1-14:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

Copy BibTex To Clipboard

@InProceedings{zeuner_et_al:LIPIcs.TYPES.2022.14,
  author =	{Zeuner, Max and M\"{o}rtberg, Anders},
  title =	{{A Univalent Formalization of Constructive Affine Schemes}},
  booktitle =	{28th International Conference on Types for Proofs and Programs (TYPES 2022)},
  pages =	{14:1--14:24},
  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.2022.14},
  URN =		{urn:nbn:de:0030-drops-184574},
  doi =		{10.4230/LIPIcs.TYPES.2022.14},
  annote =	{Keywords: Affine Schemes, Homotopy Type Theory and Univalent Foundations, Cubical Agda, Constructive Mathematics}
}
Document
DOI: 10.4230/LIPIcs.CSL.2022.11
Synthetic Integral Cohomology in Cubical Agda

Authors: Guillaume Brunerie, Axel Ljungström, and Anders Mörtberg

Published in: LIPIcs, Volume 216, 30th EACSL Annual Conference on Computer Science Logic (CSL 2022)

Abstract
This paper discusses the formalization of synthetic cohomology theory in a cubical extension of Agda which natively supports univalence and higher inductive types. This enables significant simplifications of many proofs from Homotopy Type Theory and Univalent Foundations as steps that used to require long calculations now hold simply by computation. To this end, we give a new definition of the group structure for cohomology with ℤ-coefficients, optimized for efficient computations. We also invent an optimized definition of the cup product which allows us to give the first complete formalization of the axioms needed to turn the integral cohomology groups into a graded commutative ring. Using this, we characterize the cohomology groups of the spheres, torus, Klein bottle and real/complex projective planes. As all proofs are constructive we can then use Cubical Agda to distinguish between spaces by computation.
Cite as

Guillaume Brunerie, Axel Ljungström, and Anders Mörtberg. Synthetic Integral Cohomology in Cubical Agda. In 30th EACSL Annual Conference on Computer Science Logic (CSL 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 216, pp. 11:1-11:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

Copy BibTex To Clipboard

@InProceedings{brunerie_et_al:LIPIcs.CSL.2022.11,
  author =	{Brunerie, Guillaume and Ljungstr\"{o}m, Axel and M\"{o}rtberg, Anders},
  title =	{{Synthetic Integral Cohomology in Cubical Agda}},
  booktitle =	{30th EACSL Annual Conference on Computer Science Logic (CSL 2022)},
  pages =	{11:1--11:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-218-1},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{216},
  editor =	{Manea, Florin and Simpson, Alex},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CSL.2022.11},
  URN =		{urn:nbn:de:0030-drops-157310},
  doi =		{10.4230/LIPIcs.CSL.2022.11},
  annote =	{Keywords: Synthetic Homotopy Theory, Cohomology Theory, Cubical Agda}
}
Document
DOI: 10.4230/LIPIcs.CSL.2020.14
Unifying Cubical Models of Univalent Type Theory

Authors: Evan Cavallo, Anders Mörtberg, and Andrew W Swan

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

Abstract
We present a new constructive model of univalent type theory based on cubical sets. Unlike prior work on cubical models, ours depends neither on diagonal cofibrations nor connections. This is made possible by weakening the notion of fibration from the cartesian cubical set model, so that it is not necessary to assume that the diagonal on the interval is a cofibration. We have formally verified in Agda that these fibrations are closed under the type formers of cubical type theory and that the model satisfies the univalence axiom. By applying the construction in the presence of diagonal cofibrations or connections and reversals, we recover the existing cartesian and De Morgan cubical set models as special cases. Generalizing earlier work of Sattler for cubical sets with connections, we also obtain a Quillen model structure.
Cite as

Evan Cavallo, Anders Mörtberg, and Andrew W Swan. Unifying Cubical Models of Univalent Type Theory. In 28th EACSL Annual Conference on Computer Science Logic (CSL 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 152, pp. 14:1-14:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

Copy BibTex To Clipboard

@InProceedings{cavallo_et_al:LIPIcs.CSL.2020.14,
  author =	{Cavallo, Evan and M\"{o}rtberg, Anders and Swan, Andrew W},
  title =	{{Unifying Cubical Models of Univalent Type Theory}},
  booktitle =	{28th EACSL Annual Conference on Computer Science Logic (CSL 2020)},
  pages =	{14:1--14:17},
  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.2020.14},
  URN =		{urn:nbn:de:0030-drops-116578},
  doi =		{10.4230/LIPIcs.CSL.2020.14},
  annote =	{Keywords: Cubical Set Models, Cubical Type Theory, Homotopy Type Theory, Univalent Foundations}
}
Document
DOI: 10.4230/LIPIcs.TYPES.2015.5
Cubical Type Theory: A Constructive Interpretation of the Univalence Axiom

Authors: Cyril Cohen, Thierry Coquand, Simon Huber, and Anders Mörtberg

Published in: LIPIcs, Volume 69, 21st International Conference on Types for Proofs and Programs (TYPES 2015) (2018)

Abstract
This paper presents a type theory in which it is possible to directly manipulate $n$-dimensional cubes (points, lines, squares, cubes, etc.) based on an interpretation of dependent type theory in a cubical set model. This enables new ways to reason about identity types, for instance, function extensionality is directly provable in the system. Further, Voevodsky's univalence axiom is provable in this system. We also explain an extension with some higher inductive types like the circle and propositional truncation. Finally we provide semantics for this cubical type theory in a constructive meta-theory.
Cite as

Cyril Cohen, Thierry Coquand, Simon Huber, and Anders Mörtberg. Cubical Type Theory: A Constructive Interpretation of the Univalence Axiom. In 21st International Conference on Types for Proofs and Programs (TYPES 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 69, pp. 5:1-5:34, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

Copy BibTex To Clipboard

@InProceedings{cohen_et_al:LIPIcs.TYPES.2015.5,
  author =	{Cohen, Cyril and Coquand, Thierry and Huber, Simon and M\"{o}rtberg, Anders},
  title =	{{Cubical Type Theory: A Constructive Interpretation of the Univalence Axiom}},
  booktitle =	{21st International Conference on Types for Proofs and Programs (TYPES 2015)},
  pages =	{5:1--5:34},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-030-9},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{69},
  editor =	{Uustalu, Tarmo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TYPES.2015.5},
  URN =		{urn:nbn:de:0030-drops-84754},
  doi =		{10.4230/LIPIcs.TYPES.2015.5},
  annote =	{Keywords: univalence axiom, dependent type theory, cubical sets}
}
Any Issues?
X

Feedback on the Current Page

CAPTCHA

Thanks for your feedback!

Feedback submitted to Dagstuhl Publishing

Could not send message

Please try again later or send an E-mail
© 2023-2026 Schloss Dagstuhl – LZI GmbH Schloss Dagstuhl – LZI GmbH About DROPS Imprint Privacy Contact