License: Creative Commons Attribution 3.0 Unported license (CC BY 3.0)
When quoting this document, please refer to the following
DOI: 10.4230/LIPIcs.TLCA.2015.226
URN: urn:nbn:de:0030-drops-51669
URL: http://dagstuhl.sunsite.rwth-aachen.de/volltexte/2015/5166/
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Hirschowitz, André ; Hirschowitz, Tom ; Tabareau, Nicolas

Wild omega-Categories for the Homotopy Hypothesis in Type Theory

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Abstract

In classical homotopy theory, the homotopy hypothesis asserts that the fundamental varpi-groupoid construction induces an equivalence between topological spaces and weak varpi-groupoids. In the light of Voevodsky's univalent foundations program, which puts forward an interpretation of types as topological spaces, we consider the question of transposing the homotopy hypothesis to type theory. Indeed such a transposition could stand as a new approach to specifying higher inductive types. Since the formalisation of general weak varpi-groupoids in type theory is a difficult task, we only take a first step towards this goal, which consists in exploring a shortcut through strict varpi-categories.
The first outcome is a satisfactory type-theoretic notion of strict varpi-category, which has hsets of cells in all dimensions. For this notion, defining the 'fundamental strict varpi-category' of a type seems out of reach. The second outcome is an 'incoherently strict' notion of type-theoretic varpi-category, which admits arbitrary types of cells in all dimensions. These are the 'wild' varpi-categories of the title. They allow the definition of a 'fundamental wild varpi-category' map, which leads to our (partial) homotopy hypothesis for type theory (stating an adjunction, not an equivalence).
All of our results have been formalised in the Coq proof assistant. Our formalisation makes systematic use of the machinery of coinductive types.

BibTeX - Entry

@InProceedings{hirschowitz_et_al:LIPIcs:2015:5166,
  author =	{Andr{\'e} Hirschowitz and Tom Hirschowitz and Nicolas Tabareau},
  title =	{{Wild omega-Categories for the Homotopy Hypothesis in Type Theory}},
  booktitle =	{13th International Conference on Typed Lambda Calculi and Applications (TLCA 2015)},
  pages =	{226--240},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-87-3},
  ISSN =	{1868-8969},
  year =	{2015},
  volume =	{38},
  editor =	{Thorsten Altenkirch},
  publisher =	{Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{http://drops.dagstuhl.de/opus/volltexte/2015/5166},
  URN =		{urn:nbn:de:0030-drops-51669},
  doi =		{10.4230/LIPIcs.TLCA.2015.226},
  annote =	{Keywords: Homotopy Type theory; Omega-categories; Coinduction; Homotopy hypothesis}
}

Keywords: Homotopy Type theory; Omega-categories; Coinduction; Homotopy hypothesis
Collection: 13th International Conference on Typed Lambda Calculi and Applications (TLCA 2015)
Issue Date: 2015
Date of publication: 15.06.2015

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