- #1
Avatrin
- 245
- 6
I am currently trying to understand the isomorphism theorems. The issue I am having is that I am struggling to find a way to think about them.
In Stillwell's Elements of Algebra, I found a way to understand the first theorem ([itex]\frac{G}{ker \phi} \simeq I am \phi[/itex] for any homomorphism [itex]\phi:G\rightarrow G'[/itex]). It was proven in terms of set functions (since there is a one-to-one correspondence between the elements [itex]e \in I am \phi[/itex] and [itex]\phi^{-1}(e)[/itex]). However, the second and third theorems are not even shown. Also, my curriculum is taken from Fraleigh's A First Course in Abstract Algebra. There, the first isomorphism theorem is longer than just the isomorphism between [itex]\frac{G}{ker \phi}[/itex] and [itex]Im\phi[/itex]; He adds that there is a unique isomorphism [itex]\mu: G/ker\phi \rightarrow \phi[G][/itex] such that [itex]\phi(x) = \mu(\gamma(x))[/itex] for each [itex]x \in G[/itex]. Here, [itex]\gamma[/itex] is the canonical homomorphism from G to [itex]\frac{G}{ker\phi}[/itex].
I still do not understand what the canonical homomorphism is since it is not in the index of the book. More importantly, I am really having a hard time just thinking about the definitions involved. I can see a proof, and understand why each step is accurate. Yet, it is too abstract for me to process.
This has happened once before when I was learning measure- and integration theory. I couldn't understand anything for months until one day I read a definition of the Lebesgue integral in Euclidean space, and suddenly everything just "clicked"; Within a week I could understand, rather than just know, the entire curriculum. I am hoping for another one of those moments before exam.
I have the same problem now with certain aspects of abstract algebra. They generally involve factor groups and/or mappings. So, I have a suspicion that if I "get" the isomorphism theorems, the rest will connect.
In Stillwell's Elements of Algebra, I found a way to understand the first theorem ([itex]\frac{G}{ker \phi} \simeq I am \phi[/itex] for any homomorphism [itex]\phi:G\rightarrow G'[/itex]). It was proven in terms of set functions (since there is a one-to-one correspondence between the elements [itex]e \in I am \phi[/itex] and [itex]\phi^{-1}(e)[/itex]). However, the second and third theorems are not even shown. Also, my curriculum is taken from Fraleigh's A First Course in Abstract Algebra. There, the first isomorphism theorem is longer than just the isomorphism between [itex]\frac{G}{ker \phi}[/itex] and [itex]Im\phi[/itex]; He adds that there is a unique isomorphism [itex]\mu: G/ker\phi \rightarrow \phi[G][/itex] such that [itex]\phi(x) = \mu(\gamma(x))[/itex] for each [itex]x \in G[/itex]. Here, [itex]\gamma[/itex] is the canonical homomorphism from G to [itex]\frac{G}{ker\phi}[/itex].
I still do not understand what the canonical homomorphism is since it is not in the index of the book. More importantly, I am really having a hard time just thinking about the definitions involved. I can see a proof, and understand why each step is accurate. Yet, it is too abstract for me to process.
This has happened once before when I was learning measure- and integration theory. I couldn't understand anything for months until one day I read a definition of the Lebesgue integral in Euclidean space, and suddenly everything just "clicked"; Within a week I could understand, rather than just know, the entire curriculum. I am hoping for another one of those moments before exam.
I have the same problem now with certain aspects of abstract algebra. They generally involve factor groups and/or mappings. So, I have a suspicion that if I "get" the isomorphism theorems, the rest will connect.