License: Creative Commons Attribution 4.0 International license (CC BY 4.0)
When quoting this document, please refer to the following
DOI: 10.4230/LIPIcs.FSCD.2023.18
URN: urn:nbn:de:0030-drops-180029
URL: http://dagstuhl.sunsite.rwth-aachen.de/volltexte/2023/18002/
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Bocquet, Rafaël ; Kaposi, Ambrus ; Sattler, Christian

For the Metatheory of Type Theory, Internal Sconing Is Enough

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LIPIcs-FSCD-2023-18.pdf (0.9 MB)

Abstract

Metatheorems about type theories are often proven by interpreting the syntax into models constructed using categorical gluing. We propose to use only sconing (gluing along a global section functor) instead of general gluing. The sconing is performed internally to a presheaf category, and we recover the original glued model by externalization.
Our method relies on constructions involving two notions of models: first-order models (with explicit contexts) and higher-order models (without explicit contexts). Sconing turns a displayed higher-order model into a displayed first-order model.
Using these, we derive specialized induction principles for the syntax of type theory. The input of such an induction principle is a boilerplate-free description of its motives and methods, not mentioning contexts. The output is a section with computation rules specified in the same internal language. We illustrate our framework by proofs of canonicity and normalization for type theory.

BibTeX - Entry

@InProceedings{bocquet_et_al:LIPIcs.FSCD.2023.18,
  author =	{Bocquet, Rafa\"{e}l and Kaposi, Ambrus and Sattler, Christian},
  title =	{{For the Metatheory of Type Theory, Internal Sconing Is Enough}},
  booktitle =	{8th International Conference on Formal Structures for Computation and Deduction (FSCD 2023)},
  pages =	{18:1--18:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-277-8},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{260},
  editor =	{Gaboardi, Marco and van Raamsdonk, Femke},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/opus/volltexte/2023/18002},
  URN =		{urn:nbn:de:0030-drops-180029},
  doi =		{10.4230/LIPIcs.FSCD.2023.18},
  annote =	{Keywords: type theory, presheaves, canonicity, normalization, sconing, gluing}
}

Keywords: type theory, presheaves, canonicity, normalization, sconing, gluing
Collection: 8th International Conference on Formal Structures for Computation and Deduction (FSCD 2023)
Issue Date: 2023
Date of publication: 28.06.2023

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