Find All Transitive G-Sets Up to Isomorphism w/ Subgroups of G

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Discussion Overview

The discussion revolves around the characterization of transitive G-sets in relation to subgroups of a group G, specifically exploring whether all transitive G-sets can be determined by identifying subgroups of G. The context includes theoretical aspects of group theory and representations.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant suggests that any transitive G-set is isomorphic to the coset space of some subgroup of G, using G = S_3 as an example.
  • Another participant agrees but clarifies that the coset space of a subgroup is not necessarily a quotient group if the subgroup is not normal.
  • A third participant notes that since a G-set is not necessarily a group, the isomorphic coset space also does not have to be a group.
  • A fourth participant points out that the notation used for coset spaces resembles that of quotient groups, indicating a potential confusion in terminology.

Areas of Agreement / Disagreement

Participants generally agree on the relationship between transitive G-sets and coset spaces, but there is some contention regarding the terminology and implications of coset spaces not being quotient groups.

Contextual Notes

The discussion highlights the distinction between G-sets and groups, as well as the implications of subgroup normality on the structure of coset spaces. There is also a potential ambiguity in notation that may affect understanding.

daveyinaz
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I read in a book on groups and representations that any transitive [tex]G[/tex]-set is isomorphic to the coset space of some subgroup of [tex]G[/tex].
Does this mean we can determine all transitive [tex]G[/tex]-sets up to isomorphism simply by finding all subgroups of [tex]G[/tex]?

Just want to make sure that if this is the case that I have in my mind the right idea, so we take [tex]G = S_3[/tex], then all transitive [tex]G[/tex]-sets are up to isomorphism...
[tex]G / \{e\}, G / \langle (12) \rangle , G / \langle (132) \rangle , G / G[/tex]?

Note I do realize that [tex]\langle (13) \rangle[/tex] is also a subgroup of [tex]S_3[/tex] but the way I see it the coset space would be the same as [tex]G / \langle (12) \rangle[/tex]
 
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That's correct, except that the coset space of a subgroup of G is not in general a quotient group (since the subgroup may not be normal)
 
Well that would make sense right? Since a G-set isn't necessarily a group...and if it's isomorphic to some coset space, then that coset space isn't a group either.
 
Yup, but writing

[tex] G / \{e\}, G / \langle (12) \rangle , G / \langle (132) \rangle , G / G[/tex]

This is notation for quotient groups. If H is a subgroup of G, the set of cosets is often denoted cos(G:H)
 

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