Normal Subgroups: Why Every Kernel is a Homomorphism

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SUMMARY

Every normal subgroup is the kernel of some homomorphism, specifically through the construction of quotient groups. In this discussion, it is established that for a normal subgroup H of a group G, one can define a homomorphism from G to the quotient group G/H. The kernel of this homomorphism is precisely the normal subgroup H. This relationship is fundamental in group theory and is emphasized in algebra texts.

PREREQUISITES
  • Understanding of group theory concepts, specifically normal subgroups.
  • Familiarity with homomorphisms and their properties.
  • Knowledge of quotient groups and their significance in algebra.
  • Basic skills in mathematical rigor and proof construction.
NEXT STEPS
  • Study the definition and properties of normal subgroups in detail.
  • Learn about homomorphisms and how to construct them in various algebraic structures.
  • Explore the concept of quotient groups and their applications in group theory.
  • Review examples of kernels of homomorphisms to solidify understanding of the relationship between kernels and normal subgroups.
USEFUL FOR

Students of abstract algebra, mathematicians focusing on group theory, and anyone seeking to deepen their understanding of the relationship between normal subgroups and homomorphisms.

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Homework Statement


Expain why every normal subgroup is the kernel of some homomorphism.


The Attempt at a Solution


Every kernel is a normal subgroup but the reverse I can't show rigorously. It seems possible how to show?
 
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What's the obvious map from G to G/N? What's its kernel?
 
I would have thought that would be easy- it's the direction emphasised in Algebra texts! Of course, this says "some" homomorphism- you have to pick the homomorphism carefully.

If H is a normal subgroup G, then we can define the "quotient group", G/H. There is an obvious homomorphism from G to H. What is the kernel of that homomorphism?

Darn, I had to stop in the middle to take a telephone call and morphism got in in front of me!
 

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