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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).

3 votes
2 answers
333 views

Is there a relative Pachner theorem?

Consider an $n$-dimensional PL manifold $P$ together with a closed subpolyhedron $P_0$ such that there exists a finite combinatorial triangulation of $P$ that restricts to a triangulation of $P_0$. …
Daniel Moskovich's user avatar
0 votes

Decide a manifold via its boundary

I'm wondering whether there isn't a much easier argument for 2-dimensional case, without using Seifert-van Kampen or the classification of surfaces (which is a middling hard theorem). Fix the boundar …
Daniel Moskovich's user avatar
2 votes

Quandle colorings under Reidemeister moves

No. For example, form a small loop with an R1 move on a strand coloured $x$, imagine the whole rest of the knot inside a small ball, and pass that ball on a loop-the-loop through the R1 loop. Then pe …
Daniel Moskovich's user avatar
6 votes

Generalised linking numbers (where they shouldn't be)

You'd think the definition of linking number would be common knowledge, wouldn't you? Actually, it's surprising how few places treat the topic carefully. The best references I know are: H. Schubert …
Daniel Moskovich's user avatar
3 votes

Can you do surgery on framed tangles?

You can cut out a collection of 3-balls (a regular neighbourhood of the tangle), and glue them back in a different way. Such modifications are a part of the Montesinos trick. Montesinos uses them to p …
Daniel Moskovich's user avatar
8 votes
Accepted

Rational homology spheres and knots

For Question 1, I believe that the answer follows from: Montesinos, José M. Surgery on links and double branched covers of $S^3$. Knots, groups, and 3-manifolds (Papers dedicated to the memory of R. …
Daniel Moskovich's user avatar
4 votes

Compelling evidence that two basepoints are better than one

The most convincing example I have found of "two basepoints being better than one" is the incorrect statement of the main result of the following paper: Garoufalidis, Stavros, and Andrew Kricker. "A …
Daniel Moskovich's user avatar
1 vote

Difference between Alexander polynomial and Blanchfield pairing

Clearly the signature, and more generally the Tristram-Levine signatures, would be needed.
Daniel Moskovich's user avatar
6 votes

Surgery diagram for the Seifert-Weber space

As pointed out by Ian Agol in the comments, the Seifert-Weber space is the 5-fold cyclic branched cover of the Whitehead link complement. You can therefore: Untie the Whitehead link using $\pm 1$ fr …
Daniel Moskovich's user avatar
8 votes
2 answers
1k views

Difference between Alexander polynomial and Blanchfield pairing

For a Seifert matrix $V$ of a knot $K$, the Alexander module has presentation matrix $V-tV^T$. The determinant of this matrix is the Alexander polynomial, which is the order of the Alexander module. I …
Daniel Moskovich's user avatar
8 votes
2 answers
858 views

Are there any very hard unlinks?

This question is closely related to a question of Gowers: Are there any very hard unknots? . I'm thinking about how to create interesting knots from small numbers of local moves on unlinks. The "stand …
Daniel Moskovich's user avatar
25 votes
3 answers
2k views

What are the implications of the simple loop conjecture?

Drew Zemke recently posted a preprint on arXiv proving the Simple Loop Conjecture for 3-manifolds modeled on Sol. Simple Loop Conjecture: Consider a 2-sided immersion $F\colon\, \Sigma\rightarrow M …
Daniel Moskovich's user avatar
23 votes

In knot theory: Benefits of working in $S^3$ instead of $\mathbb{R}^3$?

This is a nice question! Knot theory is in fact knot-complement theory, and a knot complement in S3 is a compact 3-manifold, while a knot complement in R3 is an open 3-manifold. Compact (or closed) 3- …
Daniel Moskovich's user avatar
9 votes
2 answers
669 views

Does every knot contain all four vertices of an isosceles trapezoid?

I ask this question with some trepidation, because it may be trivial and/or of entirely recreational interest. Erika Pannwitz proved in 1933 that every non-trivial knot contains a quadrisecant (four p …
Daniel Moskovich's user avatar
9 votes
2 answers
641 views

Is more alternating always better?

While thinking about this interesting question asked by Dylan Thurston, it occured to me that in every case that I know, the closer a knot diagram is to being alternating, the better its properties. F …
Daniel Moskovich's user avatar

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