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In [[mathematical logic]] and [[computer science]], '''homotopy type theory''' ('''HoTT''') attempts to give an account of the semantics of [[intensional type theory]] using the framework of (abstract) [[homotopy theory]], in particular [[Quillen model category|Quillen model categories]] and [[weak factorization system]]s. Conversely, intensional type theory forms a logic ([[internal language]]) for homotopy theory. | |||
== Development == | |||
{{expand section|date=September 2013}} | |||
The [[Institute for Advanced Study]] held a [http://www.math.ias.edu/sp/univalent special year] for intensive work on developing homotopy type theory in the academic year 2012-2013, jointly organised by [[Steve Awodey]], [[Thierry Coquand]] and [[Vladimir Voevodsky]], which numerous mathematicians and computer scientists attended. | |||
Out of this, a book, ''[http://homotopytypetheory.org/book/ Homotopy Type Theory]'', was born. Unusually for a mathematics text, it was developed collaboratively and in the open on [[GitHub]], is released under a [[Creative Commons license]] that allows people to [[fork (software development)|fork]] their own version of the book, and is both purchasable in print and downloadable free of charge. | |||
Also, unusually, key parts of the mathematics were implemented in the computer proof assistant [[Coq]]<ref>{{cite web|url=https://github.com/HoTT/HoTT|title=Homotopy Type Theory github repository}}</ref> and [[Agda (programming language)|Agda]],<ref>{{cite web|url=https://github.com/HoTT/HoTT-Agda|title=Homotopy Type Theory Agda files}}</ref> where Agda is broadly equivalent to Coq but has a greater emphasis on functional programming than on constructing proofs through tactics. In both cases, type checking—or, viewed another way, computer proof verification—guarantees that the proofs were valid deductions, assuming that the proof assistant used was implemented correctly. | |||
Open questions include a computational interpretation of homotopy type theory. Work is also underway to investigate new types of computer proof assistants with the goal of better supporting homotopy type theory. | |||
== Interpretation == | |||
{{see also|Curry–Howard correspondence}} | |||
{| class=wikitable | |||
! Intensional type theory !! Homotopy theory | |||
|- | |||
| types, <math>A</math> || spaces | |||
|- | |||
| terms, <math>a</math> || maps | |||
|- | |||
| <math>a:A</math> || <math>a\in A</math> | |||
|- | |||
| [[dependent type]], <math>x:A</math> ⊢ <math> B(x)</math> || [[fibration]], <math>B \to A</math> | |||
|- | |||
| [[identity type]], <math>\mathrm{Id}_A(a,b)</math> || [[path space]] | |||
|- | |||
| <math>p:\mathrm{Id}_A(a,b)</math> || [[Path (topology)|path]], <math>p:a\mapsto b</math> | |||
|- | |||
| <math>\alpha:\mathrm{Id}_{\mathrm{Id}_A(a,b)}(p,q)</math> || [[homotopy]], <math>\alpha:p\Rightarrow q</math> | |||
|} | |||
== See also == | |||
* [[weak ω-groupoid]] | |||
* [[Homotopy hypothesis]] | |||
* [[Univalence axiom]] | |||
* [[Vladimir Voevodsky]] – Initiator of the ''Univalent Foundations of Mathematics'' research program. | |||
* [[Calculus of constructions]] | |||
* [[Intuitionistic type theory]] | |||
* [[Curry–Howard isomorphism]] | |||
== References and further reading == | |||
* [http://homotopytypetheory.org/book/ ''Homotopy Type Theory: Univalent Foundations of Mathematics'']. The Univalent Foundations Program. [[Institute for Advanced Study]]. | |||
* [[Steve Awodey]] (2010). "[http://www.andrew.cmu.edu/user/awodey/preprints/TTH.pdf Type theory and homotopy]". To appear. | |||
* Martin Hofmann and [[Thomas Streicher]] (1996), [http://www.mathematik.tu-darmstadt.de/~streicher/venedig.ps.gz The groupoid interpretation of type theory], in Sambin, Giovanni (ed.) et al., Twenty-five years of constructive type theory. Proceedings of a congress, Venice, Italy, October 19–21, 1995. | |||
* Michael A. Warren (2008), [http://www.math.ias.edu/~mwarren/Papers/phd.pdf Homotopy theoretic aspects of constructive type theory], Ph.D. thesis, Carnegie Mellon University. | |||
* S. Awodey and M. A. Warren (2009), [http://www.andrew.cmu.edu/user/awodey/preprints/homotopy.pdf Homotopy theoretic models of identity types], Mathematical Proceedings of the Cambridge Philosophical Society. | |||
* Egbert Rijke (2012) [http://hottheory.files.wordpress.com/2012/08/hott2.pdf Homotopy Type Theory], Masters Thesis, Utrecht University. | |||
== References == | |||
<references /> | |||
== External links == | |||
* [http://www.homotopytypetheory.org/ Homotopy Type Theory] | |||
* {{nlab|id=homotopy+type+theory|title=Homotopy type theory}} | |||
* [http://www.math.ias.edu/~vladimir/Site3/Univalent_Foundations.html Vladimir Voevodsky's webpage on the Univalent Foundations] | |||
* [http://www.andrew.cmu.edu/user/awodey/htt.html Homotopy Type Theory and the Univalent Foundations of Mathematics] by Steve Awodey | |||
* [http://video.ias.edu/univalent/awodey "Constructive Type Theory and Homotopy"] – Video lecture by Steve Awodey at the [[Institute for Advanced Study]] | |||
* [https://groups.google.com/forum/#!forum/homotopytypetheory Homotopy Type Theory Google Group] | |||
* [irc://irc.freenode.net/##hott Homotopy Type Theory IRC channel] | |||
[[Category:Type theory]] | |||
[[Category:Homotopy theory]] | |||
Revision as of 00:00, 23 April 2013
In mathematical logic and computer science, homotopy type theory (HoTT) attempts to give an account of the semantics of intensional type theory using the framework of (abstract) homotopy theory, in particular Quillen model categories and weak factorization systems. Conversely, intensional type theory forms a logic (internal language) for homotopy theory.
Development
The Institute for Advanced Study held a special year for intensive work on developing homotopy type theory in the academic year 2012-2013, jointly organised by Steve Awodey, Thierry Coquand and Vladimir Voevodsky, which numerous mathematicians and computer scientists attended.
Out of this, a book, Homotopy Type Theory, was born. Unusually for a mathematics text, it was developed collaboratively and in the open on GitHub, is released under a Creative Commons license that allows people to fork their own version of the book, and is both purchasable in print and downloadable free of charge.
Also, unusually, key parts of the mathematics were implemented in the computer proof assistant Coq[1] and Agda,[2] where Agda is broadly equivalent to Coq but has a greater emphasis on functional programming than on constructing proofs through tactics. In both cases, type checking—or, viewed another way, computer proof verification—guarantees that the proofs were valid deductions, assuming that the proof assistant used was implemented correctly.
Open questions include a computational interpretation of homotopy type theory. Work is also underway to investigate new types of computer proof assistants with the goal of better supporting homotopy type theory.
Interpretation
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| Intensional type theory | Homotopy theory |
|---|---|
| types, | spaces |
| terms, | maps |
| dependent type, ⊢ | fibration, |
| identity type, | path space |
| path, | |
| homotopy, |
See also
- weak ω-groupoid
- Homotopy hypothesis
- Univalence axiom
- Vladimir Voevodsky – Initiator of the Univalent Foundations of Mathematics research program.
- Calculus of constructions
- Intuitionistic type theory
- Curry–Howard isomorphism
References and further reading
- Homotopy Type Theory: Univalent Foundations of Mathematics. The Univalent Foundations Program. Institute for Advanced Study.
- Steve Awodey (2010). "Type theory and homotopy". To appear.
- Martin Hofmann and Thomas Streicher (1996), The groupoid interpretation of type theory, in Sambin, Giovanni (ed.) et al., Twenty-five years of constructive type theory. Proceedings of a congress, Venice, Italy, October 19–21, 1995.
- Michael A. Warren (2008), Homotopy theoretic aspects of constructive type theory, Ph.D. thesis, Carnegie Mellon University.
- S. Awodey and M. A. Warren (2009), Homotopy theoretic models of identity types, Mathematical Proceedings of the Cambridge Philosophical Society.
- Egbert Rijke (2012) Homotopy Type Theory, Masters Thesis, Utrecht University.
References
External links
- Homotopy Type Theory
- Template:Nlab
- Vladimir Voevodsky's webpage on the Univalent Foundations
- Homotopy Type Theory and the Univalent Foundations of Mathematics by Steve Awodey
- "Constructive Type Theory and Homotopy" – Video lecture by Steve Awodey at the Institute for Advanced Study
- Homotopy Type Theory Google Group
- Homotopy Type Theory IRC channel