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11 votes
1 answer
579 views

What is the connection between Lurie's definition of shape and Čech homotopy?

It seems there are many subtly different notions of the shape of a topological space (and, more generally, toposes). For instance, Lurie [Higher topos theory] defines this one: Definition 1. The shap …
16 votes
2 answers
674 views

How to formulate the univalence axiom without universes?

The standard formulation of the univalence axiom for a universe type $U$ is that, for all $X : U$ and $Y : U$, the canonical map $(X =_U Y) \to (X \simeq Y)$ is an equivalence. As we (usually) cannot …
15 votes
2 answers
2k views

Modern versions of Verdier's hypercovering theorem?

Let $\mathcal{C}$ be a small category equipped with a terminal object $1$ and a Grothendieck topology. (Assume $\mathcal{C}$ also has pullbacks, if it is more convenient.) The following is a simplicia …
6 votes
0 answers
283 views

What are the Čech-local equivalences of (simplicial pre)sheaves?

Let $\mathcal{C}$ be small category and let $J$ be a Grothendieck topology on $\mathcal{C}$. The Čech model structure on $[\mathcal{C}^\mathrm{op}, \mathbf{sSet}]$ is defined to be the left Bousfield …