User David Rydh

80 votes

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What do epimorphisms of (commutative) rings look like?

answered Oct 6, 2009 at 23:35

37 votes

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When is fiber dimension upper semi-continuous?

answered Oct 8, 2009 at 16:20

34 votes

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Why are unramified maps not required to be locally of finite presentation?

answered May 11, 2015 at 21:33

28 votes

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Can a quotient ring R/J ever be flat over R?

answered Oct 9, 2009 at 15:42

23 votes

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If the direct image of f preserves coherent sheaves on noetherian schemes, how to show f is proper?

answered Oct 8, 2014 at 11:09

20 votes

Does a scheme have a "separification"?

answered Oct 31, 2009 at 0:39

18 votes

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Is there an example of a scheme X whose reduction X_red is affine but X is not affine?

answered Oct 5, 2009 at 0:19

17 votes

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Do line bundles descend to coarse moduli spaces of Artin stacks with finite inertia?

answered May 9, 2015 at 7:37

15 votes

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coarse moduli space of DM stacks

answered Feb 10, 2010 at 4:46

13 votes

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Weil divisors on non Noetherian schemes

answered Oct 2, 2009 at 16:14

11 votes

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Is there an example of a variety over the complex numbers with no embedding into a smooth variety?

answered Oct 8, 2009 at 16:47

11 votes

When a smooth algebra is regular?

answered Oct 8, 2015 at 18:45

11 votes

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Algebraic cycles, Chow spaces and Hilbert-Chow morphisms

answered Aug 14, 2017 at 7:45

11 votes

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Ferrand pushouts for algebraic stacks

answered Aug 21, 2020 at 20:15

10 votes

Is $\mathcal{D} \bigl( \mathrm{QCoh}(\mathfrak{X}) \bigr)$ compactly generated?

answered May 31, 2014 at 15:22

10 votes

Finite Hausdorff spaces

answered Oct 8, 2009 at 0:05

9 votes

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Milnor excision for algebraic stacks

answered Aug 28, 2020 at 14:04

7 votes

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Is there an example of an algebraic stack whose closed points have affine stabilizers but whose diagonal is not affine?

answered Oct 2, 2009 at 2:50

7 votes

Do pushouts along universal homeomorphisms exist?

answered Feb 10, 2010 at 5:00

7 votes

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Approximation of stacks / algebraic spaces

answered Feb 10, 2010 at 6:01

7 votes

Is every integral epimorphism of commutative rings surjective?

answered Feb 10, 2011 at 8:36

7 votes

universal property of blow up for stacks?

answered Feb 6, 2013 at 19:04

6 votes

algebraization theorems

answered Feb 6, 2013 at 8:57

5 votes

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Les deux théorèmes d'existence en théorie formelle des modules

answered Feb 5, 2013 at 14:32

5 votes

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Universal homeomorphism of stacks and etale sites

answered Aug 15, 2017 at 8:45

5 votes

About Fulton's Intersection theory Appendix Lemma A 4.1

answered Sep 29, 2022 at 21:07

4 votes

Gluing along closed subschemes

answered May 19, 2022 at 9:17

3 votes

Is there a non-quotient stack with affine stabilizers whose good moduli space is a geometric point?

answered Sep 30, 2020 at 9:35

3 votes

Functors on rigid tensor categories.

answered Jul 23 at 9:26

2 votes

Points of a weakly locally separated algebraic space

answered Oct 2, 2009 at 21:36

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31 Answers

What do epimorphisms of (commutative) rings look like?

When is fiber dimension upper semi-continuous?

Why are unramified maps not required to be locally of finite presentation?

Can a quotient ring R/J ever be flat over R?

If the direct image of f preserves coherent sheaves on noetherian schemes, how to show f is proper?

Does a scheme have a "separification"?

Is there an example of a scheme X whose reduction X_red is affine but X is not affine?

Do line bundles descend to coarse moduli spaces of Artin stacks with finite inertia?

coarse moduli space of DM stacks

Weil divisors on non Noetherian schemes

Is there an example of a variety over the complex numbers with no embedding into a smooth variety?

When a smooth algebra is regular?

Algebraic cycles, Chow spaces and Hilbert-Chow morphisms

Ferrand pushouts for algebraic stacks

Is $\mathcal{D} \bigl( \mathrm{QCoh}(\mathfrak{X}) \bigr)$ compactly generated?

Finite Hausdorff spaces

Milnor excision for algebraic stacks

Is there an example of an algebraic stack whose closed points have affine stabilizers but whose diagonal is not affine?

Do pushouts along universal homeomorphisms exist?

Approximation of stacks / algebraic spaces

Is every integral epimorphism of commutative rings surjective?

universal property of blow up for stacks?

algebraization theorems

Les deux théorèmes d'existence en théorie formelle des modules

Universal homeomorphism of stacks and etale sites

About Fulton's Intersection theory Appendix Lemma A 4.1

Gluing along closed subschemes

Is there a non-quotient stack with affine stabilizers whose good moduli space is a geometric point?

Functors on rigid tensor categories.

Points of a weakly locally separated algebraic space