# Tagged Questions

For questions on knot theory, the study of mathematical knots

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### Computing knot/link groups

The knot group of a knot $K$ is the fundamental group of $\mathbb R^3 \smallsetminus K$; that is, the set of possibly self-crossing closed paths (starting and ending at any single point in space) ...
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### Equivalence of knots: ambient isotopy vs. homeomorphism

I am looking into knot theory and have found two different definitions stating that two knots $K_1$ and $K_2$ are equivalent, namely the concept of an ambient isotopy: These two knots are ambient ...
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### Linking Number $0$ When One Knot is a Boundary

I am given two smooth knots $K$ and $L$ embedded in $\mathbb{R}^3$. I am also given that $K$ is the boundary of an oriented, compact surface disjoint from $L$, call it $S$. I must prove that the ...
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### Introduction to subfactor theory

I have almost no knowledge about subfactor theory but I would like to understand what it is. As a self-learner, I do not know where to start. Could you suggest introductory text/paper/book to study ...
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### The Crossing Number of a family of graphs which contain the complete bipartite graphs.

Let $p,q$ and $r$ be positive integers greater than $0$ with $q\neq r$. Suppose that $H$ is a finite connected graph without loops or multiedges on $p$ vertices with $q$ vertices of degree $r$, $r$ ...
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### figure-8 knot complement

The figure-8 knot seen as a 2-bridge knot with two maxima and two minima of the height function, has a complement in $S^3$ with one 0-handle,two 1-handles, two 2-handles and a 3-handle which cancels ...
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### Knots from the boundary of Möbius strips

A Möbius strip with one half twist has the unknot as its boundary. One with two half twists has a link of two unknots. One with three half twists has the trefoil knot as its boundary. Years ago, I ...
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### Ambient isotopy taking a polygon knot to another polygon knot

Let me define that a polygon knot means a knot K of which all point belongs to some line segment which is a subset of K. Let me ask if knot theory has some proof for that: For all pair ( K1, K2 ) ...
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### Are the generators of the braid group conjugates?

In his classic paper on Hecke algebra representations of braid groups from 1987, Vaughan Jones makes the claim that "the various generators $\sigma_i$ are all conjugate." How does one see this? I ...
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### Proving trefoil group is isomorphic to a fundamental group.

From this document exercise 2.13 states: Show that the trefoil knot group is isomorphic to the group $\langle a,b \space | \space a^3 = b^2 \rangle$. From Fact 2.9 (and also the fact that ...
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### homeomorphic two spheres embedded in $\mathbb{R}^4$

Let $A$ and $A'$ be two annuli in $\mathbb{R}^3$. Suppose $A$ has $n$ half twists and $A'$ is with $m$ half twists, where $m$ and $n$ are even and $m\ne n$. It is clear that the surface resulting by ...
A surface-knot is a closed connected surface embedded in the Euclidean 4-space $\mathbb{R}^4$. We consider the projection of the surface-knot into $\mathbb{R}^3$ with the singularity set contains of ...
Suppose that $K$ is a non-trivial, alternating knot. Is it possible that $\det K = 1$ where $\det K=\Delta_K(-1)$? Using knotinfo, I checked that all non-trivial alternating knots with crossing less ...