The Stacks project

Lemma 39.17.5. Let $S$ be a scheme. Let $(U, R, s, t, c)$ be a groupoid scheme over $S$. Let $p \in U \times _ S U$ be a point. Denote $R_ p$ the scheme theoretic fibre of $j = (t, s) : R \to U \times _ S U$. If $R_ p \not= \emptyset $, then the action

\[ G_{0, \kappa (p)} \times _{\kappa (p)} R_ p \longrightarrow R_ p \]

(see Lemma 39.17.4) which turns $R_ p$ into a $G_{\kappa (p)}$-torsor over $\kappa (p)$.

Proof. The action is a pseudo-torsor by the lemma cited in the statement. And if $R_ p$ is not the empty scheme, then $\{ R_ p \to p\} $ is an fpqc covering which trivializes the pseudo-torsor. $\square$

Comments (0)

Post a comment

Your email address will not be published.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.

In order to prevent bots from posting comments, we would like you to prove that you are human. You can do this by filling in the name of the current tag in the following input field. As a reminder, this is tag 04Q3. Beware of the difference between the letter 'O' and the digit '0'.