Levels in the toposes of simplicial sets and cubical sets
Abstract
The essential subtoposes of a fixed topos form a complete lattice, which gives rise to the notion of a level in a topos. In the familiar example of simplicial sets, levels coincide with dimensions and give rise to the usual notions of n-skeletal and n-coskeletal simplicial sets. In addition to the obvious ordering, the levels provide a stricter means of comparing the complexity of objects, which is determined by the answer to the following question posed by Bill Lawvere: when does n-skeletal imply k-coskeletal? This paper answers this question for several toposes of interest to homotopy theory and higher category theory: simplicial sets, cubical sets, and reflexive globular sets. For the latter, n-skeletal implies (n+1)-coskeletal but for the other two examples the situation is considerably more complicated: n-skeletal implies (2n-1)-coskeletal for simplicial sets and 2n-coskeletal for cubical sets, but nothing stronger. In a discussion of further applications, we prove that n-skeletal cyclic sets are necessarily (2n+1)-coskeletal.
Keywords
Cite
@article{arxiv.1003.5944,
title = {Levels in the toposes of simplicial sets and cubical sets},
author = {Carolyn Kennett and Emily Riehl and Michael Roy and Michael Zaks},
journal= {arXiv preprint arXiv:1003.5944},
year = {2011}
}
Comments
This paper subsumes earlier work of the first, third, and fourth authors. 19 pages