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Achim Krause
  • Member for 8 years, 8 months
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53 votes
Accepted

Is there any use for $\sin(\sin x)$?

38 votes
Accepted

Simply-connected rational homology spheres

37 votes
Accepted

If $\Omega X \simeq \Omega Y$ then is $X \simeq Y$ for $X,Y$ simply connected?

32 votes
Accepted

What is the group of pointed homotopy classes of maps from $S^3 \times S^3$ to $S^3$?

28 votes

What should I call a "differential" which cubes, rather than squares, to zero?

21 votes
Accepted

Is $[X, \_]$ a homology theory?

21 votes
Accepted

Does the isomorphic of the fundamental groups imply the existence of a mapping inducing an isomorphism?

18 votes
Accepted

Is $SU(3)/SO(3)$ cobordant with a mapping torus?

16 votes

What is the first interesting matric Toda bracket in the stable homotopy of the sphere?

16 votes

Which singular homology classes can be represented by embedded manifolds?

16 votes
Accepted

When is the augmentation ideal projective as RG-module?

15 votes
Accepted

Hairy ball theorem for odd-dimensional spheres

14 votes
Accepted

loop space of a finite CW-complex

13 votes

Simplest example of non-trivial Toda bracket in spaces

13 votes

Homology equivalence and isomorphism on $\pi_1$ not enough for homotopy equivalence?

12 votes
Accepted

Motivation for the definition of complex orientable cohomology theory

10 votes

In the not necessarily abelian cat setting, is there a Grothendieck spectral sequence for computing the homotopy of a composition of derived functors?

10 votes
Accepted

RIng that is flat over a subring as a right module but not as a left module

9 votes
Accepted

Is every map from a simplicial complex to a sphere homotopic to a simplicial map to the boundary of a k-simplex?

9 votes

Is there a definition of reduced $E_\infty$ ring?

9 votes

Is the cohomology ring $H^*(BG,\mathbb{Z})$ generated by Euler classes?

8 votes

Does a non-singular matrix have a large minor with disjoint rows and columns and full rank?

8 votes
Accepted

($1$-)pullbacks of Kan complexes

8 votes
Accepted

Where does this clever choice of differential come from? (calculating $\mathrm{H}^1_{\mathrm{dR}}(E/k))$

8 votes

Embedding an icosahedron

7 votes

Higher homotopy groups of irreducible 3-manifolds

7 votes
Accepted

$(B\mathbb Z/p^{\infty})^{\wedge}_p\rightarrow (BS^1)^{\wedge}_p$ induced by inclusion is an equivalence

7 votes

Given $f: X \to Y$, $g: X \to Z$, when does it exists $h: Y \to Z$ such that $hf \simeq g$?

7 votes

A very elementary question on the definition of sheaf on a site

6 votes

Integral versus real (universal) characteristic classes