Semantics of higher inductive types

[Michael Shulman <shu...@sandiego.edu>]

The following long-awaited paper is now available:

Semantics of higher inductive types
Peter LeFanu Lumsdaine, Mike Shulman
https://arxiv.org/abs/1705.07088

From the abstract:

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 specializes 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 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.