Example of Codimension-1 Manifolds that are not Isotopic.?

In summary, the conversation is about understanding how to describe the knot group Pi_1(S^3-K) as a handlebody. There is confusion about this because of unclear old notes. The process involves embedding a thickened K in S^3 and using a graph-theoretic description. The representation of the knot as a handlebody involves assigning equivalences between 0-handles, 1-handles, and 2-handles. The generators of Pi_1(S^3-K) are the edges of the knot and the relations are determined by applying the del. operator on each face. Suggestions for clarification are welcomed.
  • #1
Bacle
662
1
Hi, Everyone:

A question on knots, please; comments,references

appreciated. The main points of confusion are noted

with a ***:


1)I am trying to understand how to describe the knot

group Pi_1(S^3-K) as a handlebody ( this is not the

Wirtinger presentation; this is from some old notes

(which are not too clear now). This is what I have

so far:


We clearly start by embedding a thickened

K in S^3 as e(K). ( I imagine there is an assumed

orientation, but I can't tell where it comes from).

Topologically, S^3 is clearly the compactification

of R^3.

We then have a graph-theoretic description of e(K)

in terms of edges {e_i} and vertices {v_i}.


We then define a representation of the knot

as a handlebody (***) by setting up the equivalences:


0-handles <--> Closed neighborhoods of 00

1-handles <--> Holes in the embedding e(K)

2-handles <--> crossings in e(K)


We take the above equivalence to define relations

on the faces :(***)




The generators of Pi_1(S^3-K) are given by the

edges e_i of the knot, and the relations are given

by applyng the del. operator on each of the faces.


Thanks For any Suggestions.
 
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  • #2
My Bad: I mixed up two posts. Please Ignore the Title.
 
  • #3
Never Mind, I got it.
 

1. What is a codimension-1 manifold?

A codimension-1 manifold is a mathematical concept that refers to a space that can be described by a single coordinate system. It has a dimension that is one less than the dimension of the space it is embedded in.

2. What does it mean for two manifolds to be isotopic?

Two manifolds are considered isotopic if they can be smoothly deformed into one another without any tearing or self-intersections. This is a topological property and does not involve any cutting or gluing of the manifolds.

3. Can you give an example of codimension-1 manifolds that are not isotopic?

One example would be a circle and a figure-eight shape. Both are codimension-1 manifolds in two-dimensional space, but they cannot be smoothly deformed into one another without creating self-intersections.

4. How can we prove that two codimension-1 manifolds are not isotopic?

To prove that two manifolds are not isotopic, we can use invariants such as the Euler characteristic or the fundamental group. If these invariants differ for the two manifolds, then they are not isotopic.

5. Why is the concept of codimension-1 manifolds and isotopy important in mathematics?

Codimension-1 manifolds and isotopy are important concepts in mathematics as they allow us to classify and distinguish between different types of spaces. They also have applications in fields such as topology, geometry, and physics.

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