The Stacks project

Remark 98.9.19. Notwithstanding the warning in Remark 98.9.18 there are some cases where Lemma 98.9.17 can be used without causing ambiguity. We give a list. In each case we omit the verification of assumptions (1) and (2) and we give references which imply (3) and (4). Here is the list:

  1. $\mathcal{Q} = $“locally of finite type”, $\mathcal{R} = \emptyset $, and $\mathcal{P} =$“relative dimension $\leq d$”. See Morphisms of Spaces, Definition 65.33.2 and Morphisms of Spaces, Lemmas 65.34.4 and 65.34.3.

  2. $\mathcal{Q} =$“locally of finite type”, $\mathcal{R} = \emptyset $, and $\mathcal{P} =$“locally quasi-finite”. This is the case $d = 0$ of the previous item, see Morphisms of Spaces, Lemma 65.34.6. On the other hand, properties (3) and (4) are spelled out in Morphisms of Spaces, Lemma 65.34.7.

  3. $\mathcal{Q} = $“locally of finite type”, $\mathcal{R} = \emptyset $, and $\mathcal{P} =$“unramified”. This is Morphisms of Spaces, Lemma 65.38.10.

  4. $\mathcal{Q} =$“locally of finite presentation”, $\mathcal{R} =$“flat and locally of finite presentation”, and $\mathcal{P} =$“flat”. See More on Morphisms of Spaces, Theorem 74.22.1 and Lemma 74.22.2. Note that here $W(\mathcal{P}, f)$ is always exactly the set of points where the morphism $f$ is flat because we only consider this open when $f$ has $\mathcal{Q}$ (see loc.cit.).

  5. $\mathcal{Q} =$“locally of finite presentation”, $\mathcal{R} =$“flat and locally of finite presentation”, and $\mathcal{P}=$“étale”. This follows on combining (3) and (4) because an unramified morphism which is flat and locally of finite presentation is étale, see Morphisms of Spaces, Lemma 65.39.12.

  6. Add more here as needed (compare with the longer list at More on Groupoids, Remark 40.6.3).


Comments (0)

There are also:

  • 2 comment(s) on Section 98.9: Immersions of algebraic stacks

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Your email address will not be published.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 06M5. Beware of the difference between the letter 'O' and the digit '0'.