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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
2
answers
1k
views
Geometrization for 3-manifolds that contain two-sided projective planes
Often when people write about the geometrization conjecture they assume (for simplicity) that the manifold is orientable. I never seriously thought of non-orientable 3-manifolds, but while reading Mor …
16
votes
0
answers
642
views
Approximating homeomorphisms of 2-disk by diffeomorphisms
Any homeomorphism of a compact surface can be approximated by diffeomorphisms.
Is there a parametrized version of this result, where the parameter space is an $n$-disk?
In other words, if $S$ is a com …
20
votes
3
answers
2k
views
Homotopy groups of spaces of embeddings
Let $\mathrm{Emb}(M, N)$ be the space of smooth embeddings of a closed manifold $M$ into a manifold $N$ equipped with smooth compact-open topology.
Question 1. Are there conditions ensuring that t …
9
votes
0
answers
281
views
Extending smooth triangulation
Can one always extend a smooth triangulation from a smooth submanifold $S$ to the ambient manifold $M$? (For simplicity both $S$ and $M$ are compact without boundary). Is the extension possible when $ …
5
votes
1
answer
361
views
Whitney sum formula for topological Pontryagin classes
Is there a Whitney sum formula for topological rational Pontryagin classes? I thought the answer is yes, but now I cannot find a reference. Is it even true? The PL case would also be of interest.
4
votes
0
answers
78
views
Implicit function theorem for PL maps
Let $K$ be a PL triangulation of a closed manifold and $f: K\to\mathbb R^k$ be a PL map. Equivalently, $f$ is a map that becomes linear on every simplex after subdividing. Suppose $v$ is a vertex in t …
14
votes
3
answers
1k
views
Irreducible homology 3-spheres that bound smooth contractible manifolds
Some examples of irreducible homology 3-spheres that bound smooth contractible 4-manifolds are listed in the comment to problem 4.2 in Kirby's problem list, and all of them happen to occur among the …
9
votes
2
answers
828
views
Hyperbolic $3$-manifold groups that embed in compact Lie groups
Is there a closed hyperbolic $3$-manifold whose fundamental group is isomorphic to a subgroup of some compact Lie group?
It is known that every surface group can be embedded into any semisimple conne …
12
votes
1
answer
466
views
Finitely presented group in which every element is conjugate to its square
Does there exist a nontrivial finitely presented group in which every element is conjugate to its square? Is this an open problem?
Motivation: Jahren proved in [Geom Dedicata (2010)] that if $M$ is a …
4
votes
0
answers
103
views
Convex subsets of infinite dimensional spaces up homeomorphism
Let $C$ be a convex, infinite-dimensional, non-locally-compact subset of a separable Frechet space.
If $C$ is a closed subset (or more generally, if $C$ is completely metrizable), then it is known t …
4
votes
1
answer
458
views
Codimension zero embeddings and diffeomorphism groups
Let $V$ be a smooth manifold obtained by attaching the ``open collar'' $[0,1)\times \partial N$ to a compact smooth manifold $N$ along the boundary. Let $\mathrm{Emb}(N, V)$ be the space of embeddings …
9
votes
1
answer
909
views
Diffeomorphism group of the 2-sphere with $C^0$ topology
What is known about the homeomorphism (or homotopy) type of the group of $C^\infty$ diffeomorphisms of $S^2$ equipped with $C^0$ topology?
The group is the image of the inclusion $\mathrm{Diff}(S^2)\ …
8
votes
0
answers
296
views
Spaces that never separate the Hilbert cube
I am interested in topological spaces such that whenever the space embeds into the Hilbert cube, the image of the embedding has a path-connected complement.
Any finite dimensional space has this prop …
8
votes
1
answer
696
views
Hyperbolic 3-manifolds with no geometrically finite structure
Does there exist a compact hyperbolic 3-manifold $M$ that is not diffeomorphic to a geometrically finite hyperbolic manifold? If yes, can such $M$ have incompressible boundary?
I think the answer sho …
17
votes
1
answer
654
views
Groups with finitely generated center
Does every group with a finite classifying space have finitely generated center?
Remarks:
If $G$ is a finitely generated group with infinitely generated center $Z(G)$,
then the quotient $G/Z(G)$ i …