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Semantics of higher inductive types

Published online by Cambridge University Press:  17 June 2019

PETER LEFANU LUMSDAINE
Affiliation:
Department of Mathematics, Stockholm University, Stockholm, SE-10691, Sweden. e-mail: p.l.lumsdaine@gmail.com
MICHAEL SHULMAN
Affiliation:
Department of Mathematics, University of San Diego, 5998 Alcala Park, Sandiego, CA 92110, U.S.A. e-mail: shulman@sandiego.edu
Corresponding

Abstract

Higher inductive types are a class of type-forming rules, introduced to provide basic (and not-so-basic) homotopy-theoretic constructions in a type-theoretic style. They have proven very fruitful for the “synthetic” development of homotopy theory within type theory, as well as in formalising ordinary set-level mathematics in type theory. In this paper, we construct models of a wide range of higher inductive types in a fairly wide range of settings.

We introduce the notion of cell monad with parameters: a semantically-defined scheme for specifying homotopically well-behaved notions of structure. We then show that any suitable model category has weakly stable typal initial algebras for any cell monad with parameters. When combined with the local universes construction to obtain strict stability, this specialises to give models of specific higher inductive types, including spheres, the torus, pushout types, truncations, the James construction and general localisations.

Our results apply in any sufficiently nice Quillen model category, including any right proper, simplicially locally cartesian closed, simplicial Cisinski model category (such as simplicial sets) and any locally presentable locally cartesian closed category (such as sets) with its trivial model structure. In particular, any locally presentable locally cartesian closed (∞, 1)-category is presented by some model category to which our results apply.

Type
Research Article
Copyright
© Cambridge Philosophical Society 2019

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Footnotes

This material is based on research sponsored by The United States Air Force Research Laboratory under agreement number FA9550-15-1-0053. The U.S. Government is authorised to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the author and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the United States Air Force Research Laboratory, the U.S. Government, or Carnegie Mellon University. The research presented here was also partly funded by the Swedish Research Council (VR) Grant 2015-03835 Constructive and category-theoretic foundations of mathematics.

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