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The study of differentiable manifolds and differentiable maps. One fundamental problem is that of classifying manifolds up to diffeomorphism. Differential topology is what Poincaré understood as topology or “analysis situs”.

5 votes
Accepted

Question about exotic spheres

A exotic sphere is (by definition) a differentiable manifold. So if you want to consider the tetrahedron, you have to specify, what differentiability at one of the edges means. As soon as you specifie …
HenrikRüping's user avatar
3 votes

Artin groups whose graphs differ by one edge and coverings

Let $A_{\Gamma'}$ be the group asoociated to any graph $\Gamma'$. Concerning your first question I can show that there is a short exact sequence $$1\rightarrow F \rightarrow A_{\Gamma \setminus e}\r …
HenrikRüping's user avatar
7 votes
Accepted

Criteria for extending vector field on sphere to ball

View $B^{n}$ as $(S^{n-1}\times[0,1])/(S^{n-1}\times \{1\})$. This means that an extension of a map from $B^{n}$ to somewhere is just an extension to $S^{n-1}\times [0,1]$ which is constant on the oth …
HenrikRüping's user avatar
3 votes
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Topology of maps between fibers of vector bundles

If both bundles were trivial, say $X\times \mathbb{R}^n\rightarrow X$ and $Y\times \mathbb{R}^n\rightarrow Y$ one could just take $X\times Y\times M(m,n,\mathbb{R})$. Different choices of trivializati …
HenrikRüping's user avatar