Loading [MathJax]/extensions/tex2jax.js

The Stacks project

7.52 Points and topologies

Recall from Section 7.32 that given a functor $p = u : \mathcal{C} \to \textit{Sets}$ we can define a stalk functor

\[ \textit{PSh}(\mathcal{C}) \longrightarrow \textit{Sets}, \mathcal{F} \longmapsto \mathcal{F}_ p. \]

Definition 7.52.1. Let $\mathcal{C}$ be a category. Let $J$ be a topology on $\mathcal{C}$. A point $p$ of the topology is given by a functor $u : \mathcal{C} \to \textit{Sets}$ such that

  1. For every covering sieve $S$ on $U$ the map $S_ p \to (h_ U)_ p$ is surjective.

  2. The stalk functor $\mathop{\mathit{Sh}}\nolimits (\mathcal{C}) \to \textit{Sets}$, $\mathcal{F} \to \mathcal{F}_ p$ is exact.


Comments (0)


Your email address will not be published. Required fields are marked.

In your comment you can use Markdown and LaTeX style mathematics (enclose it like $\pi$). A preview option is available if you wish to see how it works out (just click on the eye in the toolbar).

Unfortunately JavaScript is disabled in your browser, so the comment preview function will not work.

All contributions are licensed under the GNU Free Documentation License.