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Ingo Blechschmidt
  • Member for 9 years, 6 months
  • Last seen more than a week ago
222 votes
12 answers
34k views

Is there an introduction to probability theory from a structuralist/categorical perspective?

215 votes
15 answers
56k views

Why worry about the axiom of choice?

  • 27.4k
109 votes
89 answers
27k views

Tweetable Mathematics

  • 23.6k
101 votes
1 answer
14k views

A proof for $\dim(R[T])=\dim(R)+1$ without prime ideals?

94 votes
10 answers
28k views

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

77 votes
5 answers
4k views

Can the Lawvere fixed point theorem be used to prove the Brouwer fixed point theorem?

70 votes
9 answers
18k views

Relating Category Theory to Programming Language Theory

63 votes
4 answers
9k views

What's there to do in category theory?

  • 8,860
50 votes
4 answers
7k views

How to make Ext and Tor constructive?

49 votes
6 answers
6k views

What is Yoneda's Lemma a generalization of?

47 votes
2 answers
6k views

Ring-theoretic characterization of open affines?

  • 4,792
42 votes
5 answers
4k views

Several Topos theory questions

40 votes
5 answers
3k views

Are submersions of differentiable manifolds flat morphisms?

38 votes
2 answers
3k views

Recent fundamental new directions in PDEs

  • 5,012
37 votes
4 answers
4k views

Understanding the countable ordinals up to $\epsilon_{0}$

  • 1,425
35 votes
4 answers
4k views

What is an $(\infty,1)$-topos, and why is this a good setting for doing differential geometry?

  • 8,042
31 votes
3 answers
3k views

What is the theory of local rings and local ring homomorphisms?

  • 13.3k
31 votes
2 answers
3k views

What can be expressed in and proved with the internal logic of a topos?

  • 7,907
29 votes
7 answers
4k views

"Sums-compact" objects = f.g. objects in categories of modules?

  • 5,342
26 votes
0 answers
1k views

derived category of equivariant coherent sheaves and fixed points

26 votes
5 answers
3k views

Why would one expect a derived equivalence of categories to hold?

  • 3,547
25 votes
2 answers
2k views

What are the τ-local rings for a subcanonical Grothendieck topology τ on the category of affine schemes of finite type over Spec(Z)? (specifically for τ=fppf)

  • 18.8k
24 votes
2 answers
1k views

Is there a convenient differential calculus for cojets?

  • 2,484
23 votes
8 answers
3k views

How many proofs that $\pi_n(S^n)=\mathbb{Z}$ are there?

  • 59.7k
22 votes
0 answers
898 views

What is classified by the (big) crystalline topos?

22 votes
6 answers
2k views

Where in ordinary math do we need unbounded separation and replacement?

  • 43.8k
22 votes
1 answer
1k views

Small complete categories in a Grothendieck topos

  • 59.7k
21 votes
0 answers
1k views

Schemification (schematization?) of locally ringed spaces

21 votes
2 answers
1k views

When and why do universal objects have extra properties?

21 votes
5 answers
2k views

Homological algebra and calculus (as in Newton)

  • 20.1k