Proving Non-Normality: A_4 in S_4

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In summary, the problem is to find three groups E, F, and G, where E is normal in F, F is normal in G, and E is not normal in G. The given example consists of G=A_4, F={Id, (12)(34), (13)(24), (14)(23)}, and E={Id, (12)(34)}. The attempt at a solution includes using the fact that A_4 is the kernel of S_4, meaning it is automatically normal in S_4. However, for this problem, we should focus on the given examples and determine if E is normal in F and G, and if F is normal in G.
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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?
 

1. What is A4 and S4?

A4 and S4 are mathematical notations used to represent specific groups, specifically the alternating group of order 4 and the symmetric group of order 4, respectively. These groups are often studied in abstract algebra and group theory.

2. How can you prove that A4 is non-normal in S4?

To prove that A4 is non-normal in S4, we can use the Third Isomorphism Theorem, which states that if H and K are normal subgroups of G, then H ∩ K is also a normal subgroup of G. Applying this theorem, we can show that the intersection of A4 and S4 is not a normal subgroup, thus proving that A4 is non-normal in S4.

3. Why is proving non-normality of A4 in S4 significant?

Proving non-normality of A4 in S4 is significant because it highlights the importance of understanding group structures and the relationships between different groups. It also has implications in other areas of mathematics, such as Galois theory and abstract algebra.

4. What are some alternative methods for proving non-normality of A4 in S4?

Aside from using the Third Isomorphism Theorem, other methods for proving non-normality of A4 in S4 include using the concept of conjugacy classes and examining the cycle structure of elements in A4 and S4. Another method is to use the fact that A4 is a simple group, meaning it has no non-trivial normal subgroups, and thus cannot be a normal subgroup of S4.

5. Are there any real-world applications for studying A4 in S4?

While the study of A4 in S4 may not have direct real-world applications, the concepts and techniques used in this study, such as group theory and abstract algebra, have numerous applications in fields such as physics, chemistry, and computer science. For example, group theory is essential for understanding and predicting the behavior of certain particles in physics, and in computer science, it is used in data encryption algorithms.

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