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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”.

8 votes
2 answers
384 views

Open book decompositions in dimension 4

The question about the existence of open book decompositions for a closed oriented $n$-dimensional manifold seems to be answered in all dimensions except dimension $4$, where as far as I can tell the …
ThorbenK's user avatar
  • 1,174
4 votes
1 answer
401 views

Paracompactness of Quotient by Group Action

Suppose $X$ is a metric space with a free group action by a topological group $G$, which is also a metric space, such that $\pi\colon X \to X/G$ is a fiber bundle. Does the quotient inherit the para …
ThorbenK's user avatar
  • 1,174
11 votes
2 answers
668 views

Can we embed a closed manifold into a homotopy equivalent CW complex?

Suppose $X$ is a CW complex and $M$ is a closed manifold and suppose further that there exists a homotopy equivalence $X \simeq M$. Does there exists an embedding of $M$ into $X$ (i.e. an injective (p …
ThorbenK's user avatar
  • 1,174
2 votes
1 answer
118 views

Hyperbolization with word-hyperbolic fundamental group

In Davis-Januszkiewica´s paper Hyperbolization of polyhedra it is shown that for every manifold $M$ there exists a map $N \to M$ of non-zero degree such that $N$ is aspherical (plus some more properti …
ThorbenK's user avatar
  • 1,174
6 votes

Can we embed a closed manifold into a homotopy equivalent CW complex?

While thinking about it with a friend, we came up with the following two dimensional counter example: Take the standard knot diagram of the trefoil knot (as a self-intersecting curve in $\mathbb{R}^2$ …
ThorbenK's user avatar
  • 1,174
8 votes
0 answers
219 views

Representing the fundamental class of an aspherical manifold in the bar complex

Suppose $M$ is a compact orientable aspherical manifold and $G$ its fundamental group. Is there a nice description of representatives of the fundamental class of $M$ and its dual in the (homogenous) b …
ThorbenK's user avatar
  • 1,174
8 votes

Parallelizability of 3-manifolds

Suppose we have a non-compact $3$ dimensional manifold $M$ which is spinable. Fix a CW structure of the manifold, then being spinable is equivalent to the tangent bundle being trivial on the $2$-skele …
ThorbenK's user avatar
  • 1,174
7 votes
1 answer
196 views

Lipschitz bounds and homotopy groups of diffeomorphism groups

Let $M$ denote a closed Riemannian manifold. Let $\mathrm{Diff}_0^L(M)$ denote the supspace of the identity component of the diffeomorphism group $\mathrm{Diff}_0(M)$ of diffeomorphisms with Lipschitz …
ThorbenK's user avatar
  • 1,174
9 votes
1 answer
434 views

Action of diffeomorphism group on non-vanishing vector fields

Let $M$ denote a closed manifold. Let $\Gamma(TM\setminus 0) $ denote the space of non-vanishing sections of $TM$. Note that the diffeomorphism group $\text{Diff} (M)$ acts on $\Gamma(TM\setminus 0 …
ThorbenK's user avatar
  • 1,174
10 votes
3 answers
656 views

Doubles of 2-handlebodies

Let $X$ denote a $4$-manifold with boundary obtained by adding $k_1$ $1$-handles to $B^4$ and $k_2$ many $2$-handles to the resulting manifold i.e. $X$ is an arbitrary $4$-dimensional $2$-handlebody. …
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  • 1,174
4 votes
Accepted

Doubles of 2-handlebodies

Let $X$ denote a $2$-handlebody. I claim that the inclusion $\partial X \to X$ induces a surjection on fundamental groups. Indeed, let $Y\subset X$ denote the underlying $1$-handlebody (i.e. the union …
ThorbenK's user avatar
  • 1,174
12 votes
1 answer
368 views

Fundamental group of the complement of a codimension two submanifold

Let $M$ denote an arbitrary closed, connected, n-dimensional manifold for $n\geq 4$. Does there always exist a closed (not necessarily connected!) codimension two submanifold $S \subset M$ such that $ …
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