Are the Right and Left Cosets Equal in a Group's Cayley Table?

  • Context: Undergrad 
  • Thread starter Thread starter mathsdespair
  • Start date Start date
  • Tags Tags
    Group Table
Click For Summary

Discussion Overview

The discussion revolves around the properties of left and right cosets in the context of a group's Cayley table, particularly focusing on whether there is a theorem that can determine when these cosets are equal. The conversation also touches on the multiplication of cosets and the implications of normal subgroups.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant inquires about the existence of a theorem that could indicate when right and left cosets are equal, expressing a desire to simplify their workload.
  • Several participants reference the concept of normal subgroups, suggesting that if a subgroup is normal, then the left and right cosets are equal.
  • There is a discussion about the multiplication of cosets, with one participant questioning whether cosets can simply be multiplied together and noting a potential problem mentioned by their teacher.
  • Another participant explains that while cosets can be multiplied, the result is not necessarily a coset, and emphasizes that the set of cosets does not generally form a group unless the subgroup is normal.
  • It is noted that if a subgroup is normal, the product of cosets can be simplified to a coset of the product of the elements.

Areas of Agreement / Disagreement

Participants generally agree that normal subgroups lead to equal left and right cosets, but there is no consensus on a specific theorem that addresses the equality of cosets in general. The discussion about multiplying cosets reveals some uncertainty regarding the conditions under which this operation is valid.

Contextual Notes

Limitations include the lack of specific definitions or theorems referenced in the initial inquiry, as well as the unresolved nature of the potential problems associated with multiplying cosets.

mathsdespair
Messages
16
Reaction score
0
Just by looking at the cayley table of a group and looking at its subgroups, is their a theorem or something which tells you if the right and left cosets are equal?

I have question to do and I would love to half the workload by not having to to work out the same thing twice.
Thanks
 
Physics news on Phys.org
When multiplying cosets, can you just quite simply multiply them together?
Our teacher said something about their could be a potential problem?
What could the problem be?
 
mathsdespair said:
When multiplying cosets, can you just quite simply multiply them together?
Our teacher said something about their could be a potential problem?
What could the problem be?
You can always multiply cosets, but the result is not necessarily a coset. In other words, the set of right or left cosets is not generally a group. Thus you can form the product ##aHbH##, which is the set of all elements of the form ##ah_1bh_2##, but this does not generally equal ##abH##, nor can it generally be written in the form ##gH## at all.

However, if ##H## is a normal subgroup, then the left and right cosets are the same (##aH = Ha##), so we just call them cosets, and the set of cosets does form a group. In this case, the product ##aHbH## can be simplified as follows:
$$aHbH = a(Hb)H = a(bH)H = abHH = abH$$
 
jbunniii said:
You can always multiply cosets, but the result is not necessarily a coset. In other words, the set of right or left cosets is not generally a group. Thus you can form the product ##aHbH##, which is the set of all elements of the form ##ah_1bh_2##, but this does not generally equal ##abH##, nor can it generally be written in the form ##gH## at all.

However, if ##H## is a normal subgroup, then the left and right cosets are the same (##aH = Ha##), so we just call them cosets, and the set of cosets does form a group. In this case, the product ##aHbH## can be simplified as follows:
$$aHbH = a(Hb)H = a(bH)H = abHH = abH$$

Thank you for the good explanation.
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 13 ·
Replies
13
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K