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abx
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26 votes
4 answers
2k views

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

25 votes
4 answers
1k views

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

19 votes
3 answers
966 views

Number of fixed points of an involution

19 votes
2 answers
908 views

Reference for the triple covering of A_6

16 votes
1 answer
1k views

Topological proof that a Vitali set is not Borel

16 votes
4 answers
776 views

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

14 votes
2 answers
448 views

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

14 votes
3 answers
1k views

Norms in quadratic fields

14 votes
1 answer
543 views

Rational sextic plane curves

14 votes
2 answers
1k views

Coboundary of a cup-product

14 votes
1 answer
459 views

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

13 votes
1 answer
390 views

Is the following result about congruences of lines classical?

13 votes
0 answers
262 views

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

13 votes
2 answers
517 views

Calabi-Yau threefold with an automorphism of infinite order

12 votes
2 answers
442 views

Threefolds of general type with no holomorphic forms?

11 votes
0 answers
218 views

Non-isomorphic curves with isomorphic Jacobians

10 votes
2 answers
435 views

Limit of decomposable bundles

10 votes
1 answer
255 views

Low rank vector bundles on hypersurfaces

10 votes
1 answer
852 views

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

10 votes
1 answer
673 views

Étale cohomology versus classical cohomology

9 votes
2 answers
546 views

Relations between homogeneous polynomials

9 votes
1 answer
338 views

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

8 votes
2 answers
184 views

The degree of the hypersurface of pfaffian cubic fourfolds

8 votes
3 answers
356 views

Surjectivity of differential operators with constant coefficients

7 votes
1 answer
675 views

Some special complex tori

7 votes
1 answer
524 views

Does a central extension split over some finite index subgroup?

7 votes
0 answers
332 views

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

5 votes
1 answer
136 views

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

5 votes
0 answers
211 views

Quartic surfaces with separate tritangents

5 votes
0 answers
255 views

Higher order deformations of subvarieties