Proving Non-Normality: A_4 in S_4

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SUMMARY

The discussion focuses on proving the non-normality of the subgroup E={Id, (12)(34)} within the group G=A_4, while E is normal in F={Id, (12)(34), (13)(24), (14)(23)} and F is normal in G. The relationship between these groups is established through subgroup containment, with E being a subgroup of F and F being a subgroup of G. The key takeaway is that while E is normal in F, it does not maintain this property when considered within G, illustrating the concept of subgroup normality in group theory.

PREREQUISITES
  • Understanding of group theory concepts, specifically normal subgroups.
  • Familiarity with the alternating group A_4 and symmetric group S_4.
  • Knowledge of subgroup containment and properties of subgroups.
  • Basic comprehension of group homomorphisms and kernels.
NEXT STEPS
  • Study the properties of normal subgroups in group theory.
  • Explore the structure and properties of the symmetric group S_4.
  • Investigate the relationship between kernels and normal subgroups in group homomorphisms.
  • Examine examples of non-normal subgroups in various groups.
USEFUL FOR

This discussion is beneficial for students and educators in abstract algebra, particularly those studying group theory, as well as mathematicians interested in subgroup properties and their applications.

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Homework Statement


Prove by an example, that we can find 3 groups E c F c G, where E is normal in F, F is normal in G, but E is not normal in G.
(c denotes "contained in")

Consider:
G=A_4
F={Id, (12)(34), (13)(24), (14)(23)} and
E={Id, (12)(34)}

The Attempt at a Solution


I want to use the fact that A_4 is the kernel of S_4 so automatically it is normal in S_4. But how is F related to S_4?
 
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What do you mean "A_4 is the kernel of S_4"?

Forget about S_4. Consider the examples you have been given. E is a subgroup of F which in turn is a subgroup of G. Is E normal in F? In G? Is F normal in G?
 

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