Homomorphism and Preimage: How are they related in Group Theory?

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SUMMARY

The discussion focuses on the relationship between homomorphisms and preimages in group theory, specifically addressing the homomorphism i: G → H. It establishes that for a fixed element g in G, the preimage i^−1(h) of an element h in H is defined as the set {kg | k ∈ ker i}. The proof demonstrates that if x is the preimage of h, then xg^−1 is in the kernel of i, confirming that i^−1(h) is a subset of {kg | k ∈ ker i}. Additionally, the discussion confirms that {kg | k ∈ ker i} is also a subset of i^−1(h).

PREREQUISITES
  • Understanding of group theory concepts, specifically homomorphisms.
  • Familiarity with the definition and properties of kernels in group theory.
  • Knowledge of the notation and operations involving preimages in mathematical functions.
  • Basic algebraic manipulation skills to handle group elements and their operations.
NEXT STEPS
  • Study the properties of group homomorphisms in more depth.
  • Explore examples of kernels in various groups to solidify understanding.
  • Learn about the Fundamental Theorem of Homomorphisms and its implications.
  • Investigate the relationship between isomorphisms and homomorphisms in group theory.
USEFUL FOR

This discussion is beneficial for students and educators in abstract algebra, particularly those studying group theory. It is also useful for mathematicians looking to deepen their understanding of homomorphisms and their properties.

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Homework Statement



Let i : G → H be a homomorphism of groups. Fix an element g of G and let
i(g) = h ∈ H. Show that the preimage i^−1(h) of h under i is the set
i^−1(h) = {kg | k ∈ ker i}.

Homework Equations





The Attempt at a Solution


i(ab)=i(a)i(b)
preimage is a in G such that i(a)=h
We know i(a)=h by definition of i
i(a)=h
i(a)i(a)^-1=hi(a)^-1
e=hi(a)^-1
 
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let x be the preimage of h, ie: i(x)=h=i(g),
then i(xg-1)=e, then what can you say about x??
 
It's the kernel?
 
hmm, you know xg-1 in in the kernel, then (xg-1)g is in {kg | k ∈ ker i}, so this conclude that i^−1(h) is subset of {kg | k ∈ ker i}.
now left to show is {kg | k ∈ ker i} subset of i^−1(h)
 

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