Understanding Proof: Clarifying the Relationship Between K and H

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Discussion Overview

The discussion revolves around understanding a proof related to the intersection of groups, specifically the relationship between the groups K and H. Participants are examining a particular point in the proof concerning why the intersection K ∩ H is a proper subgroup of H, and whether the problem can be approached using the Fundamental Theorem of Finitely Generated Abelian Groups.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about why K ∩ H is a proper subgroup of H based on the choice of an element y.
  • Another participant clarifies that the term "proper" is implicit and that K ∩ H is always a subgroup of either K or H, emphasizing that y not being in H indicates a proper inclusion.
  • A later reply questions whether the problem could also be approached using the Fundamental Theorem of Finitely Generated Abelian Groups.
  • Another participant asks for clarification on which theorem is being referenced, noting that the proof provided is short and straightforward.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the clarity of the proof or the applicability of the Fundamental Theorem of Finitely Generated Abelian Groups, indicating that multiple views and uncertainties remain in the discussion.

Contextual Notes

The discussion highlights a potential ambiguity in terminology regarding "proper" subgroups and the assumptions underlying the proof. There is also an unresolved inquiry about the relevance of the Fundamental Theorem of Finitely Generated Abelian Groups to the problem at hand.

Mr Davis 97
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https://imgur.com/a/jThCPLA

I'm trying to understand the proof here, and there is just one point that I get tripped up on. In the last paragraph, I'm not seeing exactly why ##K\cap H < H## based upon our choice of ##y##. Could someone explain?
 
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Mr Davis 97 said:
https://imgur.com/a/jThCPLA

I'm trying to understand the proof here, and there is just one point that I get tripped up on. In the last paragraph, I'm not seeing exactly why ##K\cap H < H## based upon our choice of ##y##. Could someone explain?
The implicite (and missing) word is "proper". ##H\cap K## is always a subgroup of either. The fact that ##y \notin H## makes it a proper inclusion. ##K\cap H \lneq H## would have been the better sign.
 
fresh_42 said:
The implicite (and missing) word is "proper". ##H\cap K## is always a subgroup of either. The fact that ##y \notin H## makes it a proper inclusion. ##K\cap H \lneq H## would have been the better sign.
Oh, I think I got it now. One more question. Could this problem also be solved with the Fundamental Theorem of Finitely Generated Abelian Groups?
 
Help me, what theorem do you mean? The proof you have is quite short and straightforward, I don't know a better one.
 

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