Isomorphic Quotient Groups: A Counterexample

In summary, when considering normal subgroups H and K of a group G, it is possible for H and K to be isomorphic while G/H and G/K are not isomorphic. This can occur when G and K are not conjugates and there exists an automorphism of G taking H to K. Additionally, the order of H and K must be chosen carefully to ensure there is more than one group of that order.
  • #1
ehrenfest
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Homework Statement


Let H and K be normal subgroups of a group G. Give an example showing that we may have H isomorphic to K while G/H is not isomorphic to G/K.


Homework Equations





The Attempt at a Solution


I don't want to look in the back of my book just yet. Can someone give me a hint?
 
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  • #2
If G and K are conjugates, then its easy to show that G/H and G/K are isomorphic, so you need to look for non-conjugate subgroups (more generally, this is true if there is an automorphism of G taking H to K). You also obviously need to pick [G:H] so that there is actually more than one group of this order.
 

1. What is an isomorphic quotient group?

An isomorphic quotient group is a mathematical concept that arises in group theory, which is the study of algebraic structures called groups. An isomorphic quotient group is formed by taking a subgroup of a given group and dividing the elements of the original group into equivalence classes based on the subgroup. The resulting quotient group is isomorphic, meaning that it has the same structure, as the original group.

2. How do you determine if two groups are isomorphic quotient groups?

Two groups are considered isomorphic quotient groups if there exists a bijective homomorphism (a function that preserves the group structure) between them. This means that the elements in the two groups can be mapped to each other in such a way that the group operations are preserved. In simpler terms, if the two groups have the same structure and can be transformed into each other without changing their group operations, then they are isomorphic quotient groups.

3. What is the significance of isomorphic quotient groups?

Isomorphic quotient groups are important in group theory because they allow us to study the structure of a group by breaking it down into simpler groups. By identifying the subgroup and the corresponding equivalence classes, we can better understand the properties and relationships within the original group. Isomorphic quotient groups also help us to classify and compare different groups.

4. Can a group have multiple isomorphic quotient groups?

Yes, a group can have multiple isomorphic quotient groups. This is because different subgroups of a group can lead to different equivalence classes and thus, different quotient groups. However, all of these quotient groups will have the same structure as the original group, just with different elements and group operations.

5. How are isomorphic quotient groups used in real-world applications?

Isomorphic quotient groups have applications in various fields such as cryptography, coding theory, and physics. In cryptography, they are used to create secure encryption algorithms. In coding theory, they are used to study error-correcting codes. In physics, they are used to study symmetry and conservation laws. Isomorphic quotient groups also have applications in other areas of mathematics, such as topology and algebraic geometry.

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