Outputs (22)

Internal Parametricity, without an Interval (2024)
Journal Article
Altenkirch, T., Chamoun, Y., Kaposi, A., & Shulman, M. (2024). Internal Parametricity, without an Interval. Proceedings of the ACM on Programming Languages, 8(POPL), 2340-2369. https://doi.org/10.1145/3632920

Parametricity is a property of the syntax of type theory implying, e.g., that there is only one function having the type of the polymorphic identity function. Parametricity is usually proven externally, and does not hold internally. Internalising it... Read More about Internal Parametricity, without an Interval.

The Münchhausen Method in Type Theory (2023)
Journal Article
Altenkirch, T., Kaposi, A., Šinkarovs, A., & Végh, T. (2023). The Münchhausen Method in Type Theory. LIPIcs, 269, https://doi.org/10.4230/LIPIcs.TYPES.2022.10

In one of his long tales, after falling into a swamp, Baron Münchhausen salvaged himself and the horse by lifting them both up by his hair. Inspired by this, the paper presents a technique to justify very dependent types. Such types reference the ter... Read More about The Münchhausen Method in Type Theory.

Should Type Theory Replace Set Theory as the Foundation of Mathematics? (2023)
Journal Article
Altenkirch, T. (2023). Should Type Theory Replace Set Theory as the Foundation of Mathematics?. Global Philosophy, 33(1), Article 21. https://doi.org/10.1007/s10516-023-09676-0

Mathematicians often consider Zermelo-Fraenkel Set Theory with Choice (ZFC) as the only foundation of Mathematics, and frequently don’t actually want to think much about foundations. We argue here that modern Type Theory, i.e. Homotopy Type Theory (H... Read More about Should Type Theory Replace Set Theory as the Foundation of Mathematics?.

Naive Type Theory (2019)
Book Chapter
Altenkirch, T. (2019). Naive Type Theory. In S. Centrone, D. Kant, & D. Sarikaya (Eds.), Reflections on the Foundations of Mathematics: Univalent Foundations, Set Theory and General Thoughts (101-136). Springer

We introduce Type Theory, including Homotopy Type Theory, as an alternative to set theory as a foundation of Mathematics emphasising the intuitive and naive understanding of its concepts.

Quotient inductive-inductive types (2018)
Book Chapter
Altenkirch, T., Capriotti, P., Dijkstra, G., Kraus, N., & Nordvall Forsberg, F. (2018). Quotient inductive-inductive types. In C. Baier, & U. Dal Lago (Eds.), FoSSaCS 2018: Foundations of Software Science and Computation Structures (293-310). Springer Publishing Company. https://doi.org/10.1007/978-3-319-89366-2_16

Higher inductive types (HITs) in Homotopy Type Theory (HoTT) allow the definition of datatypes which have constructors for equalities over the defined type. HITs generalise quotient types and allow to define types which are not sets in the sense of H... Read More about Quotient inductive-inductive types.

Towards a cubical type theory without an interval (2018)
Journal Article
Altenkirch, T., & Kaposi, A. (2018). Towards a cubical type theory without an interval. LIPIcs, 3:1-3:27. https://doi.org/10.4230/LIPIcs.TYPES.2015.3

Following the cubical set model of type theory which validates the univalence axiom, cubical type theories have been developed that interpret the identity type using an interval pretype. These theories start from a geometric view of equality. A proof... Read More about Towards a cubical type theory without an interval.

Normalisation by evaluation for type theory, in type theory (2017)
Journal Article
Altenkirch, T., & Kaposi, A. (2017). Normalisation by evaluation for type theory, in type theory. Logical Methods in Computer Science, 13(4), https://doi.org/10.23638/LMCS-13%284%3A1%292017

© Altenkirch and Kaposi. We develop normalisation by evaluation (NBE) for dependent types based on presheaf categories. Our construction is formulated in the metalanguage of type theory using quotient inductive types. We use a typed presentation henc... Read More about Normalisation by evaluation for type theory, in type theory.

Notions of anonymous existence in Martin-Löf type theory (2017)
Journal Article
Kraus, N., Escardo, M., Coquand, T., & Altenkirch, T. (in press). Notions of anonymous existence in Martin-Löf type theory. Logical Methods in Computer Science, 13(1),

As the groupoid model of Hofmann and Streicher proves, identity proofs in intensional Martin-L\"of type theory cannot generally be shown to be unique. Inspired by a theorem by Hedberg, we give some simple characterizations of types that do have uniqu... Read More about Notions of anonymous existence in Martin-Löf type theory.

Normalisation by evaluation for dependent types (2016)
Presentation / Conference Contribution
Altenkirch, T., & Kaposi, A. (2016). Normalisation by evaluation for dependent types.

We develop normalisation by evaluation (NBE) for dependent types based on presheaf categories. Our construction is formulated using internal type theory using quotient inductive types. We use a typed presentation hence there are no preterms or realiz... Read More about Normalisation by evaluation for dependent types.

Indexed containers (2015)
Journal Article
Altenkirch, T., Ghani, N., Hancock, P., McBride, C., & Morris, P. (2015). Indexed containers. Journal of Functional Programming, 25, 1-41. https://doi.org/10.1017/s095679681500009x

We show that the syntactically rich notion of strictly positive families can be reduced to a core type theory with a fixed number of type constructors exploiting the novel notion of indexed containers. As a result, we show indexed containers provide... Read More about Indexed containers.