User abx

26 votes

4 answers

2k views

The sum of two well-ordered subsets is well-ordered

set-theory ordered-groups

asked Jan 18, 2021 at 13:25

25 votes

4 answers

1k views

$\operatorname{PSL}(2,\mathbb{F}_p) $ does not embed in $\mathfrak{S}_p$ for $p>11$

gr.group-theory finite-groups

asked Aug 21, 2021 at 13:43

19 votes

3 answers

976 views

Number of fixed points of an involution

ag.algebraic-geometry

asked Dec 12, 2019 at 9:42

19 votes

2 answers

908 views

Reference for the triple covering of A_6

reference-request gr.group-theory finite-groups

asked Jan 13, 2014 at 12:31

16 votes

1 answer

1k views

Topological proof that a Vitali set is not Borel

gn.general-topology descriptive-set-theory alternative-proof

asked May 25, 2020 at 9:15

16 votes

4 answers

790 views

Meromorphic function on $\mathbb{C}$ algebraic over $\mathbb{C}(z)$

cv.complex-variables

asked Nov 18, 2021 at 16:11

14 votes

2 answers

451 views

Direct image of the structure sheaf by an endomorphism of $\mathbb{P}^2$

ag.algebraic-geometry

asked Jun 20, 2020 at 5:09

14 votes

3 answers

1k views

Norms in quadratic fields

nt.number-theory reference-request algebraic-number-theory

asked Aug 22, 2020 at 14:59

14 votes

1 answer

549 views

Rational sextic plane curves

ag.algebraic-geometry

asked Dec 15, 2020 at 10:09

14 votes

2 answers

1k views

Coboundary of a cup-product

at.algebraic-topology

asked Feb 22, 2015 at 11:34

14 votes

1 answer

459 views

Minimum degree of a variety with $H^i(X,\mathcal{O}_X)\neq 0$ for some $i$ with $0<i<\dim(X)$

ag.algebraic-geometry

asked Nov 5, 2017 at 0:04

13 votes

1 answer

390 views

Is the following result about congruences of lines classical?

ag.algebraic-geometry reference-request

asked May 15, 2018 at 5:54

13 votes

0 answers

263 views

The inequality $K_X^n\leq (-n-1)^n \chi (\mathscr{O}_X)$

ag.algebraic-geometry

asked Apr 6, 2021 at 8:12

13 votes

2 answers

522 views

Calabi-Yau threefold with an automorphism of infinite order

ag.algebraic-geometry complex-geometry

asked Feb 16, 2020 at 16:37

12 votes

2 answers

442 views

Threefolds of general type with no holomorphic forms?

ag.algebraic-geometry

asked Dec 18, 2018 at 17:00

11 votes

0 answers

218 views

Non-isomorphic curves with isomorphic Jacobians

ag.algebraic-geometry

asked Dec 25, 2019 at 15:22

10 votes

2 answers

443 views

Limit of decomposable bundles

ag.algebraic-geometry

asked Dec 6, 2017 at 6:47

10 votes

1 answer

259 views

Low rank vector bundles on hypersurfaces

ag.algebraic-geometry

asked Aug 25, 2017 at 5:45

10 votes

1 answer

855 views

Does there exist a Fano variety with torsion in $H^3$?

ag.algebraic-geometry

asked Sep 10, 2014 at 8:44

10 votes

1 answer

674 views

Étale cohomology versus classical cohomology

ag.algebraic-geometry etale-cohomology

asked Jan 21, 2015 at 10:21

9 votes

2 answers

546 views

Relations between homogeneous polynomials

ag.algebraic-geometry ac.commutative-algebra

asked Mar 19, 2019 at 20:17

9 votes

1 answer

343 views

$K_3(\mathbb{Z})$ and $\pi ^S_3$

homotopy-theory kt.k-theory-and-homology algebraic-k-theory

asked Aug 31, 2019 at 8:07

8 votes

2 answers

185 views

The degree of the hypersurface of pfaffian cubic fourfolds

ag.algebraic-geometry

asked Feb 13, 2019 at 11:00

8 votes

3 answers

357 views

Surjectivity of differential operators with constant coefficients

differential-operators

asked Nov 21, 2018 at 10:38

7 votes

1 answer

677 views

Some special complex tori

ag.algebraic-geometry

asked Nov 7, 2013 at 6:10

7 votes

1 answer

526 views

Does a central extension split over some finite index subgroup?

gr.group-theory homological-algebra

asked Jun 7, 2017 at 13:17

7 votes

0 answers

337 views

Class of a linear series in the Chow ring of $\operatorname{Sym}^d(C)$

ag.algebraic-geometry

asked Jun 17, 2021 at 10:13

5 votes

1 answer

139 views

Why is $\operatorname{U}(n,\mathbb{H})\subset \operatorname{SL}(n,\mathbb{H}) $?

matrices lie-groups quaternions

asked Feb 13 at 13:37

5 votes

0 answers

211 views

Quartic surfaces with separate tritangents

ag.algebraic-geometry

asked Dec 3, 2013 at 14:50

5 votes

0 answers

255 views

Higher order deformations of subvarieties

ag.algebraic-geometry

asked Mar 4, 2018 at 22:45

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32 Questions

The sum of two well-ordered subsets is well-ordered

$\operatorname{PSL}(2,\mathbb{F}_p) $ does not embed in $\mathfrak{S}_p$ for $p>11$

Number of fixed points of an involution

Reference for the triple covering of A_6

Topological proof that a Vitali set is not Borel

Meromorphic function on $\mathbb{C}$ algebraic over $\mathbb{C}(z)$

Direct image of the structure sheaf by an endomorphism of $\mathbb{P}^2$

Norms in quadratic fields

Rational sextic plane curves

Coboundary of a cup-product

Minimum degree of a variety with $H^i(X,\mathcal{O}_X)\neq 0$ for some $i$ with $0<i<\dim(X)$

Is the following result about congruences of lines classical?

The inequality $K_X^n\leq (-n-1)^n \chi (\mathscr{O}_X)$

Calabi-Yau threefold with an automorphism of infinite order

Threefolds of general type with no holomorphic forms?

Non-isomorphic curves with isomorphic Jacobians

Limit of decomposable bundles

Low rank vector bundles on hypersurfaces

Does there exist a Fano variety with torsion in $H^3$?

Étale cohomology versus classical cohomology

Relations between homogeneous polynomials

$K_3(\mathbb{Z})$ and $\pi ^S_3$

The degree of the hypersurface of pfaffian cubic fourfolds

Surjectivity of differential operators with constant coefficients

Some special complex tori

Does a central extension split over some finite index subgroup?

Class of a linear series in the Chow ring of $\operatorname{Sym}^d(C)$

Why is $\operatorname{U}(n,\mathbb{H})\subset \operatorname{SL}(n,\mathbb{H}) $?

Quartic surfaces with separate tritangents

Higher order deformations of subvarieties