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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).

24 votes
4 answers
4k views

Fundamental group of 3-manifold with boundary

Is it true that any finitely presented group can be realized as fundamental group of compact 3-manifold with boundary?
Anton Petrunin's user avatar
20 votes
2 answers
1k views

Rugged manifold

It is well known that any compact smooth $m$-manifold can be obtained from $m$-ball by gluing some points on the boundary. Is it still true for topological manifold? Comments: To proof the smo …
Anton Petrunin's user avatar
18 votes
2 answers
1k views

Which immersed plane curves bound an immersed disk?

I am looking for a nice answer to the following question. Which immersed plane curves bound an immersed disk? Comments. I am not sure what is a nice answer, but for sure I could make a stupid …
Anton Petrunin's user avatar
17 votes
1 answer
573 views

Simply connected slices

Assume $\Omega$ is an open set in $\mathbb R^3$ such that the intersection of $\Omega$ with any horizontal plane is simply connected. Can you prove that $\Omega$ is simply connected? (Note th …
Anton Petrunin's user avatar
16 votes
2 answers
813 views

Klee's trick --- more applications

In his "Some topological properties..." (1955), Klee gave a construction (simple and beautiful) of an isotopy $h_t\colon\mathbb{R}^{2\cdot n}\to \mathbb{R}^{2\cdot n}$ which moves any compact set $K$ …
Anton Petrunin's user avatar
15 votes
1 answer
410 views

bi-Lipschitz gluing

Let $H$ be the Heisenberg group with left invariant sub-Riemannian metric and $\varepsilon>0$ is small. Let us denote by $|x-y|_H$ the distance from $x$ to $y$ in $H$. I have a bi-Lipschitz homeomor …
Anton Petrunin's user avatar
13 votes
1 answer
562 views

Limit of homeomorphisms from square to square

Let $\square=[0,1]\times[0,1]$ be the unit square and $f\colon\square\to \square$ is a continuous map that fixes the points on the boundary. Assume $f$ is a limit of homeomorphisms $\square\to \squar …
Anton Petrunin's user avatar
13 votes
1 answer
861 views

Ramified cover of 4-sphere

Is it true that any closed oriented $4$-dimensional manifold can be obtained as a result of the following construction: Take $S^4$ with a finite collection of immersed closed 2-manifolds (with trans …
Anton Petrunin's user avatar
10 votes
1 answer
387 views

Wild half-line in a Euclidean space

Is there an $m$-dimensional simplicial complex $S$ with the following properties: The cone over $S$ is homeomorphic to $\mathbb{E}^{m+1}$. Here $\mathbb{E}^{m+1}$ denoes the $(m+1)$-dimensional Eucl …
Anton Petrunin's user avatar
9 votes
1 answer
340 views

Ramified cover of 3-ball

I it true that any connected oriented 3-manifold with nonempty boundary can be obtained as a ramified cover of 3-ball with a ramification at a link? link = a 1-dimensional submanifold with possibly …
Anton Petrunin's user avatar
6 votes
1 answer
301 views

Stable torus that is not a torus [duplicate]

Let $M$ be a closed manifold such that $M\times \mathbb{S}^1$ is a torus. Is it true that $M$ is homeomorphic to a torus?
Anton Petrunin's user avatar
3 votes
1 answer
322 views

Simplified Bing's house

Bing's house is an example of contractible 2-complex in $\mathbb{R}^3$. One may think that it is a surface without boundary that has two types of singularities: tripod curves — curves where three piec …
Anton Petrunin's user avatar