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Topology of cell complexes and manifolds, classification of manifolds (e.g. smoothing, surgery), low dimensional topology (e.g. knot theory, invariants of 4-manifolds), embedding theory, combinatorial and PL topology, geometric group theory, infinite dimensional topology (e.g. Hilbert cube manifolds, theory of retracts).

12 votes

CW structures on unitary sphere of a banach/Hilbert space

The answer is no in infinite dimension (and yes in the finite dimensional case, of course). Because the sphere in a Banach space is Baire. But an infinite dimensional CW-complex is not, being a counta …
Daniele Zuddas's user avatar
1 vote
Accepted

Homotopy of Unitary sphere in a Banach space and finite dimensional spheres

Well, it is well-known that both of $X$ and $Y$ are contractible (hence they are homotopy equivalent, this should answer your question). Notice that $Y$ is exactly the set of unit vectors of $E$. To …
Daniele Zuddas's user avatar
8 votes

Open immersions of open manifolds

This is the special case announced in the comment. We assume $M$ to be an oriented 4-manifold with the homotopy type of a 2-complex. We prove that $M$ immerses in $\mathbb{C}P^2$. In the case of comp …
Daniele Zuddas's user avatar
7 votes
Accepted

Can cobordisms of 3 or 4 manifolds be visualized by moves on kirby diagrams?

I think that a complete set of moves for cobordisms are the following: Kirby moves (that preserve the 4-manifold), handle trading (dotted circles become 0-framed 2-handles), addition/deletion of pairs …
Daniele Zuddas's user avatar
3 votes
Accepted

Existence of orientation preserving, finite order self homeomorphism on a genus 2 surface wi...

The answer is yes, as it has been remarked in the previous answers. Here is a very explicit construction. Let $T$ be the sphere $S^2 \subset \Bbb R^3$ with three disks removed. Take these three disks …
Daniele Zuddas's user avatar
0 votes

What are these compact sets called?

What about "set with piecewise smooth boundary"?
Daniele Zuddas's user avatar
2 votes

Mapping class between coverings of Riemann surfaces

This is a simple exercise and the answer is no (cf. comments of Lee Mosher and Misha). Consider the two degree-4 coverings of the torus to itself with monodromies $\omega_1, \omega_2 : \pi_1(T^2) \to …
Daniele Zuddas's user avatar
4 votes

How to specify a compact topological 4-manifold with a finite amount of data

In my understanding, I guess that the following strategy could be be attempted. Let $M$ be a closed connected orientable 4-manifold (while nonorientable 4-manifolds are doubly covered by orientable on …
Daniele Zuddas's user avatar
20 votes
2 answers
1k views

Manifolds with homeomorphic interiors

Suppose that two compact topological manifolds with boundary have homeomorphic interiors. Can we conclude that the two manifolds are homeomorphic? What happens in the smooth category?
Daniele Zuddas's user avatar
8 votes
1 answer
380 views

Second homology of mapping class group of genus 3

In a survey paper of Korkmaz it is stated that $H_2(\mathrm{Mod}_3)$ is either $\Bbb Z$ or $\Bbb Z \oplus \Bbb Z_2$, but I was not able to find out a precise computation of this group (resolving the a …
Daniele Zuddas's user avatar
2 votes

Algorithm for computing the Arf invariant of a knot

This is too long for a comment, it's just an idea for this computation. Start with a Seifert surface $F \subset \Bbb R^3$ for the knot $K$. Up to isotopy, we can assume that $F$ projects regularly to …
Daniele Zuddas's user avatar
7 votes

The boundary of a domain whose interior is diffeomorphic to the ball

First, your assumption imply that $\bar D$ is a compact smooth manifold with boundary a topological sphere (because is a simply connected homology sphere). So, $\bar D$ is a topological $n$-ball, by t …
Daniele Zuddas's user avatar
6 votes
0 answers
197 views

Surgering locally flat tori in 4-manifolds

Is there a locally flat torus in some not smoothable topological 4-manifold such that surgering on it produces a smoothable 4-manifold? Surgering means removing a tubular neighborhood and reattaching …
Daniele Zuddas's user avatar
11 votes

Morse theory in TOP and PL categories?

For TOP Morse function a reference is the classical book of Kirby and Siebenmann "Foundational essays on topological manifolds, smoothings, and triangulations" (1977). The key point is to consider the …
Daniele Zuddas's user avatar
12 votes
1 answer
812 views

Handlebody decomposition of an open 4-manifold

Let $M$ be the fake $CP^2$ (namely the closed topological 4-manifold which is homotopy equivalent but not homeomorphic to the complex projective plan). It is well-known that $M$ admits no smooth struc …
Daniele Zuddas's user avatar

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