How to abelianizing the fundamental group?

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Discussion Overview

The discussion revolves around the process of abelianizing the fundamental group of a topological space, particularly focusing on understanding the theorem that states abelianizing the fundamental group of a connected space yields its first homotopy group. Participants seek clarification on how to abelianize a group and request examples to illustrate the concept.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant states that abelianizing a fundamental group gives the first homotopy group of a connected space and seeks a clearer understanding of this theorem.
  • Another participant suggests that to abelianize a group, one must mod out by the commutator subgroup, providing a reference for further reading.
  • A third participant reiterates the theorem and explains that the abelianization results in the first homology group with integer coefficients, providing an example involving the fundamental group of the Euclidean plane minus two points.
  • A later reply indicates that a participant has not yet learned about commutator subgroups but intends to study them to better understand the discussion.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the concept of abelianization and its implications, with no consensus reached on the clarity of the theorem or the process involved.

Contextual Notes

Some participants have not yet learned about commutator subgroups, which may limit their understanding of the abelianization process. The discussion also reflects differing familiarity with the underlying concepts of homotopy and homology groups.

kakarotyjn
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There is a theorem:If |K| is connected,abelianizing its fundamental group gives the first homotopy group of K.

How to abelianize a group? And how to understand this theorem more obviously?Can anyone show me an example to see it?

I myself will think this problem for more time because I learn it just now and haven't think it much.

Thank you!:smile:
 
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kakarotyjn said:
How to abelianize a group?
Mod out by [G,G], its commutator subgroup. E.g. see here.
 
kakarotyjn said:
There is a theorem:If |K| is connected,abelianizing its fundamental group gives the first homotopy group of K.

How to abelianize a group? And how to understand this theorem more obviously?Can anyone show me an example to see it?

I myself will think this problem for more time because I learn it just now and haven't think it much.

Thank you!:smile:

The fundamental group is the first homotopy group. Abelianized, it is the first homology group with Z coefficients.

The abelianization, as Landau said, is the quotient group modulo the commutator subgroup.

Example. The Euclidean plane minus 2 points. Its fundamental group is the free group on two generators. It first homology group is the free abelian group on two generators.
 
Thank you! I haven't learned commutator subgroups,but I will pick it up now to understand it.
 

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