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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”.

6 votes
Accepted

Computing the Euler characteristic of the complex projective plane using differential topology

There is a canonical way to construct holomorphic vector fields on $\mathbb{C}P^2,$ and that way is described in Zoladek's "Monodromy Group", page 335. If you read the description, it will be pretty c …
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5 votes

Computing the Euler characteristic of the complex projective plane using differential topology

By the way, a very cool (to my mind) way of computing the Euler characteristic of $\mathbb{C}P^n$ is to treat it as the $n$-fold symmetric product of $\mathbb{C}P^1 = \mathbb{S}^2$ with itself. Then, …
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1 vote

on product of some spaces

This question (or a close relative) is discussed and answered in When factors may be cancelled in homeomorphic products?
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4 votes

Extension of a group action beyond the boundary

If you are asking for a topological action, then it would seem you can just double $M$ along the boundary. I am not sure this works in the smooth category..
Igor Rivin's user avatar
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3 votes

Circle Bundles of surfaces

See this wikipedia article on Seifert Fibered Spaces.
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18 votes

Homeomorphisms of $S^n\times S^1$

This is false for $n=1.$ The mapping class group of the torus is $SL(2, Z),$ of which the homeomorphisms you describe are but a small part - the parabolic matrices $\begin{pmatrix}1 & n\\ 0 &1\end{pma …
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3 votes

Structural stability on the circle

You can read Jaco Palis' PhD thesis. The result is presumably also in deMelo/vanStrien http://w3.impa.br/~demelo/tablecon.html EDIT Here is the link to the published version of Palis's thesis: http:// …
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9 votes

Extending a diffeomorphism of the sphere $S^2$ to the ball $D^3$

A combinatorial proof of Smale's theorem (actually a stronger theorem, which at the time of the paper cited was a conjecture of N. Kuiper) is given in the paper The space of simplexwise linear homeom …
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6 votes

Obstruction to a general S^1-action

It is a result of Atiyah-Hirzebruch (1970) that the $\hat{A}$ genus of a spin manifold with a nontrivial $S^1$ action vanishes, and a result of Herrera and Herrera that the same result, if the manifo …
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4 votes
Accepted

Set of density matrices

This is a symmetric space when equipped by the metric discussed in this question (it is Riemannian, when $p=2$). The metric is clearly invariant under the action; its other properties can be checked ( …
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0 votes

When a homeomorphism is a diffeomorphism w.r.t to a suitable smooth structure?

Just a slight addition to Danny Ruberman's answer: more example in the same vein are discussed in David Gay's note "4-manifolds which are homeomorphic but not diffeomorphic".
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11 votes
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is there a diffeomorphism with only finite orbits but of infinite order?

No, there is no such animal. This is due to Montgomery (1938), see my answer to this question: Nonperiodic points of homeomorphisms of a ball
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4 votes

Diffeomorphisms of a surface in terms of generators.

If your question is: can you present the homeotopy group in terms of generators and relations, the answer is "yes", following the work of Hatcher-Thurston, Wajnryb, and most recently M. Korkmaz, who g …
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10 votes
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Is a compact, connected, orientable 3-manifold with $\mathbb{Z}^K$ fundemental group uniquel...

NO, since the three-torus $T^3$ does not have this form. EDIT if the OP really means a free product of $\mathbb{Z}$s, so the free group $F_k,$ then the answer is YES. It is a fact (see Hempel's book, …
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2 votes

Reference request: gluing manifolds along pieces of boundary

This seems to be discussed here. (particularly page 6)
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