User Georges Elencwajg

152 votes

13 answers

22k views

Why is the fundamental group of a compact Riemann surface not free ?

asked Apr 6, 2012 at 15:40

132 votes

3 answers

21k views

When is the tensor product of two fields a field?

asked Nov 28, 2011 at 13:44

85 votes

6 answers

51k views

How many mathematicians are there?

asked Nov 14, 2009 at 8:27

80 votes

7 answers

12k views

Cubical vs. simplicial singular homology

asked Nov 1, 2009 at 10:48

75 votes

4 answers

6k views

When is a singular point of a variety ($\mathcal{C}^\infty$-) smooth?

asked May 30, 2012 at 11:52

75 votes

3 answers

9k views

Does a power series converging everywhere on its circle of convergence define a continuous function?

asked Oct 22, 2012 at 16:22

72 votes

3 answers

8k views

Where do all these projection formulas come from?

asked Jun 8, 2011 at 9:40

65 votes

1 answer

4k views

Did Bourbaki write a text on algebraic geometry?

asked Mar 20, 2015 at 9:06

42 votes

4 answers

3k views

What is the Krull dimension of the ring of holomorphic functions on a complex manifold?

asked Apr 19, 2012 at 14:51

42 votes

6 answers

6k views

Arbitrary products of schemes don't exist, do they?

asked Dec 16, 2009 at 22:09

40 votes

1 answer

3k views

Is every connected scheme path connected?

asked Oct 1, 2010 at 10:35

37 votes

3 answers

3k views

What does it mean geometrically that an element in a domain is irreducible?

asked May 4, 2011 at 10:05

35 votes

0 answers

2k views

History of the Proj construction in algebraic geometry

asked Jul 15, 2014 at 8:24

34 votes

1 answer

2k views

Mr. G.P.K.'s questions [closed]

asked Apr 1, 2011 at 10:12

34 votes

2 answers

2k views

An algebraic vector bundle is trivialized by open sets. How many does one need?

asked Dec 15, 2010 at 18:21

31 votes

2 answers

2k views

Should Krull dimension be a cardinal?

asked Jan 21, 2010 at 21:02

29 votes

1 answer

1k views

Which intrinsic invariants of a projective variety can you deduce from its Hilbert polynomials?

asked Dec 12, 2016 at 11:00

28 votes

2 answers

3k views

Is every algebraic smooth hypersurface of affine space parallelizable?

asked Jul 1, 2011 at 8:18

25 votes

2 answers

4k views

Is a universally closed morphism of schemes quasi-compact ?

asked May 3, 2010 at 12:32

23 votes

3 answers

2k views

Which vector spaces are duals ?

asked Feb 3, 2011 at 8:32

22 votes

3 answers

2k views

Is a complex manifold projective just because its blow-up at a point is ?

asked Feb 9, 2011 at 10:19

22 votes

0 answers

577 views

Are the reals really a fraction field?

asked Apr 7, 2014 at 23:12

21 votes

2 answers

2k views

What is the dimension of the product ring $\prod \mathbb Z/2^n\mathbb Z$ ?

asked Mar 12, 2012 at 12:50

21 votes

1 answer

2k views

Are the Stiefel-Whitney classes of a vector bundle the only obstructions to its being invertible?

asked Oct 18, 2010 at 12:53

21 votes

5 answers

1k views

Computation of fraction field of formal series over the integers

asked May 10, 2020 at 16:45

21 votes

1 answer

970 views

Can you give an example of two projective morphisms of schemes whose composition is not projective?

asked Nov 12, 2019 at 10:27

19 votes

0 answers

312 views

Can one properly embed a differential manifold into numerical space of double dimension? [duplicate]

asked Nov 24, 2014 at 13:03

17 votes

3 answers

1k views

Did Grothendieck introduce vertical arrows that denote morphisms?

asked Oct 31, 2011 at 13:07

17 votes

4 answers

1k views

Can one glue De Rham cohomology classes on a differential manifolds?

asked May 12, 2022 at 10:53

17 votes

1 answer

1k views

Is a direct sum of flabby sheaves flabby?

asked Jul 18, 2020 at 22:05

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50 Questions

Why is the fundamental group of a compact Riemann surface not free ?

When is the tensor product of two fields a field?

How many mathematicians are there?

Cubical vs. simplicial singular homology

When is a singular point of a variety ($\mathcal{C}^\infty$-) smooth?

Does a power series converging everywhere on its circle of convergence define a continuous function?

Where do all these projection formulas come from?

Did Bourbaki write a text on algebraic geometry?

What is the Krull dimension of the ring of holomorphic functions on a complex manifold?

Arbitrary products of schemes don't exist, do they?

Is every connected scheme path connected?

What does it mean geometrically that an element in a domain is irreducible?

History of the Proj construction in algebraic geometry

Mr. G.P.K.'s questions [closed]

An algebraic vector bundle is trivialized by open sets. How many does one need?

Should Krull dimension be a cardinal?

Which intrinsic invariants of a projective variety can you deduce from its Hilbert polynomials?

Is every algebraic smooth hypersurface of affine space parallelizable?

Is a universally closed morphism of schemes quasi-compact ?

Which vector spaces are duals ?

Is a complex manifold projective just because its blow-up at a point is ?

Are the reals really a fraction field?

What is the dimension of the product ring $\prod \mathbb Z/2^n\mathbb Z$ ?

Are the Stiefel-Whitney classes of a vector bundle the only obstructions to its being invertible?

Computation of fraction field of formal series over the integers

Can you give an example of two projective morphisms of schemes whose composition is not projective?

Can one properly embed a differential manifold into numerical space of double dimension? [duplicate]

Did Grothendieck introduce vertical arrows that denote morphisms?

Can one glue De Rham cohomology classes on a differential manifolds?

Is a direct sum of flabby sheaves flabby?