English

A stratified homotopy hypothesis

Algebraic Topology 2017-03-30 v4 Category Theory Geometric Topology

Abstract

We show that conically smooth stratified spaces embed fully faithfully into \infty-categories. This articulates a stratified generalization of the homotopy hypothesis proposed by Grothendieck. As such, each \infty-category defines a stack on conically smooth stratified spaces, and we identify the descent conditions it satisfies. These include R1\mathbb{R}^1-invariance and descent for open covers and blow-ups, analogous to sheaves for the h-topology in A1\mathbb{A}^1-homotopy theory. In this way, we identify \infty-categories as striation sheaves, which are those sheaves on conically smooth stratified spaces satisfying the indicated descent. We use this identification to construct by hand two remarkable examples of \infty-categories: Bun\mathcal{B}{\sf un}, an \infty-category classifying constructible bundles; and Exit\mathcal{E}{\sf xit}, the absolute exit-path \infty-category. These constructions are deeply premised on stratified geometry, the key geometric input being a characterization of conically smooth stratified maps between cones and the existence of pullbacks for constructible bundles.

Keywords

Cite

@article{arxiv.1502.01713,
  title  = {A stratified homotopy hypothesis},
  author = {David Ayala and John Francis and Nick Rozenblyum},
  journal= {arXiv preprint arXiv:1502.01713},
  year   = {2017}
}

Comments

84 pages; numerous corrections made; definition of constructible bundle modified to add a condition on links, ensuring existence of pullbacks (Lemma 6.1.11)

R2 v1 2026-06-22T08:23:17.621Z