Help Proving Isomorphism of a group

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    Group Isomorphism
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Discussion Overview

The discussion revolves around proving that a cyclic group is isomorphic to a ring under addition, specifically focusing on the structure of cyclic groups and their relationship to the integers modulo n. Participants explore strategies for establishing isomorphism, including the necessary conditions and definitions involved in the proof.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant notes the need to satisfy three conditions for isomorphism: being one-to-one, onto, and preserving the operation.
  • Another participant emphasizes the importance of defining an explicit isomorphism.
  • Several participants suggest defining a function \( f(g) = g^n \mod n \) to establish the isomorphism between a cyclic group \( G \) of order \( n \) and \( \mathbb{Z}_n = \{0, \ldots, n-1\} \).
  • A participant clarifies that since \( G \) is cyclic, every element can be represented as \( g^k \) for some \( 0 \leq k < n \), leading to the definition \( f(g^k) = k \).
  • There is a request for clarification on the notation and the meaning of \( g^n \mod n \) in the context of the proposed function.

Areas of Agreement / Disagreement

Participants generally agree on the approach of defining a function to demonstrate the isomorphism, but there are uncertainties regarding the specifics of the function and its implications. The discussion remains unresolved on the complete proof and the finer details of the definitions involved.

Contextual Notes

There are limitations in the clarity of the definitions and the assumptions about the cyclic group and the nature of the isomorphism being proposed. The discussion does not resolve the mathematical steps necessary to complete the proof.

Bruce Wayne1
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Hi!

I'm trying to prove a cyclic group is isomorphic to ring under addition. What the strategy I would take? How would I get it started?

Here's what I know so far:

I need to meet 3 conditions-- 1 to 1, onto, and the operation is preserved. I also know that isomorphic means that the group is homomorphic with onto and 1 to 1.
 
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Bruce Wayne said:
I'm trying to prove a cyclic group is isomorphic to ring under addition. What the strategy I would take? How would I get it started?
You need to come up with an explicit definition of an alleged isomorphism.
 
are you tring to prove a cyclic group G of order n is isomorphic to Z_n ={0,...,n-1}?Define $f(g)=g^n$ (mod n)
 
Poirot said:
are you tring to prove a cyclic group G of order n is isomorphic to Z_n ={0,...,n-1}?Define $f(g)=g^n$ (mod n)
I may be missing something. Is $f:G\to\mathbb{Z}_n$? Then what is $g^n\pmod{n}$?
 
Poirot said:
are you tring to prove a cyclic group G of order n is isomorphic to Z_n ={0,...,n-1}?Define $f(g)=g^n$ (mod n)

Yes, exactly. I want to show that a cyclic group G of order n is isomorphic to Zn.

I understand the concepts, and I know how to prove it for a relatively small n, but I haven't been able to find a completed proof online. I'd like to read it, and ask a few questions on the theory of why it works (should any arise).
 
Since $G$ is cyclic of order $n$, there exists a $g\in G$ such that every $x\in G$ can be represented as $g^k$ for some $0\le k<n$. Therefore, we can define an $f:G\to\mathbb{Z}_n$ as follows: $f(g^k)=k$. It rests to show that $f$ is one-to-one, onto and a homomorphism.
 
Evgeny.Makarov said:
I may be missing something. Is $f:G\to\mathbb{Z}_n$? Then what is $g^n\pmod{n}$?

yes sorry I mean f(g^k)=k (mod n), where g is the generator of G
 

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