User Eric Wofsey

75 votes

What are some reasonable-sounding statements that are independent of ZFC?

answered Oct 22, 2009 at 21:33

67 votes

Can anyone give me a good example of two interestingly different ordinary cohomology theories?

answered Oct 21, 2009 at 23:00

60 votes

Accepted

understanding Steenrod squares

answered Oct 13, 2009 at 22:18

58 votes

Cohomology and fundamental classes

answered Oct 20, 2009 at 22:25

44 votes

Accepted

Is every functor a composition of adjoint functors?

answered Oct 12, 2009 at 4:07

43 votes

Why does non-abelian group cohomology exist?

answered Oct 24, 2009 at 23:53

40 votes

Accepted

Is there a "simplification" functor in algebraic topology?

answered Jan 8, 2015 at 23:24

39 votes

Accepted

Whitehead for maps

answered Oct 26, 2009 at 20:51

39 votes

What is a continuous path?

answered Nov 12, 2011 at 21:37

35 votes

What are the open subsets of $\mathbb{R}^n$ that are diffeomorphic to $\mathbb{R}^n$

answered Nov 7, 2009 at 0:32

33 votes

Accepted

Maximal ideals in the ring of continuous real-valued functions on ℝ

answered Nov 3, 2009 at 0:18

32 votes

Accepted

Is there a conceptual reason why topological spaces have quotient structures while metric spaces don't?

answered Mar 6, 2013 at 12:48

28 votes

Does pointwise convergence imply uniform convergence on a large subset?

answered Nov 12, 2010 at 14:36

28 votes

Accepted

Which sequences can be extended to analytic functions? (e. g., Ackermann's function)

answered Oct 28, 2009 at 0:06

28 votes

Accepted

Are all smooth functions composites of 0-, 1-, and 2-ary functions?

answered Feb 1, 2015 at 1:32

27 votes

Accepted

Does there exist a homotopy equivalence from $\mathbb{C}P^{2n}$ to itself that reverses orientation?

answered Jul 20, 2015 at 17:21

26 votes

Accepted

Left/right exact functor "in nature" which is not a right/left adjoint

answered Feb 16, 2013 at 16:20

25 votes

Accepted

Are Thom spectra MU, MSO and K-theory spectra KU, KO modules over some truncations of the sphere spectrum?

answered Mar 13, 2013 at 2:11

25 votes

Accepted

Which partitions of $[0,1]$ are collection of level sets of a real continuous function?

answered Oct 8, 2015 at 14:59

24 votes

When $X \times Y \cong X \times Z$ implies $Y \cong Z$ (in the category of finite topological spaces)

answered May 11, 2017 at 20:40

24 votes

Accepted

Why does the naive choice of homogeneous coordinate ring of a product of projective schemes not work?

answered Apr 6, 2013 at 19:01

22 votes

Analogue to covering space for higher homotopy groups?

answered Oct 17, 2009 at 23:50

22 votes

Accepted

Cantor's theorem for presheaves?

answered Dec 22, 2014 at 3:21

21 votes

Accepted

When does $\mathbf{Top}/X$ embedd fully faithfully into $\mathbf{Top}$?

answered Nov 21, 2014 at 5:00

21 votes

Accepted

Direct limit of compact topological spaces

answered Apr 3, 2015 at 19:55

21 votes

Accepted

Are subfunctors of left exact functors also left exact?

answered Apr 1, 2013 at 17:32

20 votes

Linear transformation that preserves the determinant

answered Oct 15, 2009 at 0:30

20 votes

What is (co)homology, and how does a beginner gain intuition about it?

answered Oct 15, 2009 at 20:42

20 votes

Accepted

Does projective imply flat?

answered Jun 30, 2015 at 19:07

20 votes

Accepted

How many subsets of $[0,1)$ are there modulo null sets?

answered Mar 19, 2015 at 21:01

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265 Answers

What are some reasonable-sounding statements that are independent of ZFC?

Can anyone give me a good example of two interestingly different ordinary cohomology theories?

understanding Steenrod squares

Cohomology and fundamental classes

Is every functor a composition of adjoint functors?

Why does non-abelian group cohomology exist?

Is there a "simplification" functor in algebraic topology?

Whitehead for maps

What is a continuous path?

What are the open subsets of $\mathbb{R}^n$ that are diffeomorphic to $\mathbb{R}^n$

Maximal ideals in the ring of continuous real-valued functions on ℝ

Is there a conceptual reason why topological spaces have quotient structures while metric spaces don't?

Does pointwise convergence imply uniform convergence on a large subset?

Which sequences can be extended to analytic functions? (e. g., Ackermann's function)

Are all smooth functions composites of 0-, 1-, and 2-ary functions?

Does there exist a homotopy equivalence from $\mathbb{C}P^{2n}$ to itself that reverses orientation?

Left/right exact functor "in nature" which is not a right/left adjoint

Are Thom spectra MU, MSO and K-theory spectra KU, KO modules over some truncations of the sphere spectrum?

Which partitions of $[0,1]$ are collection of level sets of a real continuous function?

When $X \times Y \cong X \times Z$ implies $Y \cong Z$ (in the category of finite topological spaces)

Why does the naive choice of homogeneous coordinate ring of a product of projective schemes not work?

Analogue to covering space for higher homotopy groups?

Cantor's theorem for presheaves?

When does $\mathbf{Top}/X$ embedd fully faithfully into $\mathbf{Top}$?

Direct limit of compact topological spaces

Are subfunctors of left exact functors also left exact?

Linear transformation that preserves the determinant

What is (co)homology, and how does a beginner gain intuition about it?

Does projective imply flat?

How many subsets of $[0,1)$ are there modulo null sets?