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Rasmus
  • Member for 11 years, 11 months
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46 votes
3 answers
11k views

Why doesn't $0$ being a prime ideal in $\mathbb Z$ imply that $0$ is a prime number?

40 votes
7 answers
10k views

How to tell if some power of my integer matrix is the identity?

25 votes
3 answers
2k views

How to compute the series $\sum_{n=0}^\infty q^{n^2}$?

24 votes
9 answers
3k views

Reference for spectral sequences

24 votes
8 answers
6k views

"Why do I always get 1 when I keep hitting the square root button on my calculator?"

19 votes
2 answers
2k views

Is the closedness of the image of a Fredholm operator implied by the finiteness of the codimension of its image?

18 votes
1 answer
3k views

Homogeneous topological spaces

17 votes
3 answers
2k views

Is there an algebraic homomorphism between two Banach algebras which is not continuous?

16 votes
1 answer
707 views

What is the spectrum of the commutative C*-algebra I have constructed here?

15 votes
4 answers
2k views

Reference for "It is enough to specify a sheaf on a basis"?

14 votes
1 answer
275 views

What is the decategorification of a triangulated category?

12 votes
1 answer
954 views

Sanity check: Is every T-principal bundle over T trivial?

12 votes
3 answers
3k views

How to compute homotopy classes of maps on the 2-torus?

12 votes
1 answer
5k views

Does rapid decay of Fourier coefficients imply smoothness?

10 votes
2 answers
1k views

Is the group isomorphism problem decidable for abelian groups?

10 votes
1 answer
564 views

What is the commutative analogue of a $C^*$-subalgebra?

9 votes
1 answer
877 views

Does the Gelfand transformation on $\ell^1(\mathbb Z)$ possess a continuous inverse on its image?

9 votes
1 answer
2k views

Is there a trick to prove injectivity for maps out of tensor products?

9 votes
3 answers
396 views

Can we turn the functor "category ring" into a 2-functor in a natural way?

8 votes
2 answers
379 views

What is the kernel of the summation map from the direct sum to the sum?

6 votes
1 answer
264 views

Does the ring of integers have the following property?

6 votes
1 answer
1k views

Does this covariant functor really turn coproducts into products?

6 votes
2 answers
2k views

How can I find a basis for the kernel of a homomorphism on a free abelian group?

6 votes
2 answers
734 views

Why do differential forms and integrands have different transformation behaviours under diffeomorphisms?

6 votes
1 answer
350 views

Comparison of two convergence conditions for sequences of non-negative numbers

5 votes
1 answer
468 views

Is there a notion of basis for Banach spaces?

5 votes
1 answer
195 views

Is there a list of all connected $T_0$-spaces with 5 points?

5 votes
0 answers
174 views

Projective objects in compounded Abelian category

5 votes
0 answers
223 views

Non-trivial conditions for $\mathrm{Ext}^2(A,B)=0$?

5 votes
1 answer
113 views

Does $\varprojlim\ ^1$ vanish whenever it doesn't have to account for non-right exactness of $\varprojlim$?