The Stacks project

Lemma 29.32.11. Let $f : X \to S$ and $g : Y \to S$ be morphisms of schemes with the same target. Let $p : X \times _ S Y \to X$ and $q : X \times _ S Y \to Y$ be the projection morphisms. The maps from Lemma 29.32.8

\[ p^*\Omega _{X/S} \oplus q^*\Omega _{Y/S} \longrightarrow \Omega _{X \times _ S Y/S} \]

give an isomorphism.

Proof. By Lemma 29.32.10 the composition $p^*\Omega _{X/S} \to \Omega _{X \times _ S Y/S} \to \Omega _{X \times _ S Y/Y}$ is an isomorphism, and similarly for $q$. Moreover, the cokernel of $p^*\Omega _{X/S} \to \Omega _{X \times _ S Y/S}$ is $\Omega _{X \times _ S Y/X}$ by Lemma 29.32.9. The result follows. $\square$


Comments (0)

There are also:

  • 2 comment(s) on Section 29.32: Sheaf of differentials of a morphism

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Your email address will not be published.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 01V1. Beware of the difference between the letter 'O' and the digit '0'.