Group Isomorphism: Proving G Is an Odd, Ablian Group

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SUMMARY

The discussion centers on proving that a finite group \( G \) is an abelian odd group under the conditions of a specific automorphism \( \varphi \) that satisfies \( \varphi^2 = e_G \) and is fixed point free for non-identity elements. The participants confirm that \( G \) must be of odd order and establish that \( \varphi(a) = a^{-1} \) for any element \( a \neq e \), leading to the conclusion that \( G \) is abelian. A link to a proof supporting this assertion is provided, reinforcing the validity of the argument.

PREREQUISITES
  • Understanding of group theory concepts, specifically automorphisms.
  • Familiarity with the properties of finite groups and their orders.
  • Knowledge of abelian groups and their characteristics.
  • Basic algebraic notation and operations involving groups.
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  • Study the properties of automorphisms in group theory.
  • Learn about the implications of groups having fixed point free automorphisms.
  • Research the relationship between group order and abelian properties.
  • Explore additional proofs related to group isomorphism and automorphism behavior.
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This discussion is beneficial for mathematicians, particularly those specializing in abstract algebra, as well as students seeking to deepen their understanding of group theory and its applications in proving group properties.

Andrei1
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Here is a problem from some russian book of algebra:
Suppose $$G$$ is a finite group. An automorphism $$\varphi$$ "operates" on this group. This automorphism satisfies the following two conditions: 1) $$\varphi^2=e_G$$; 2) if $$a\not= e$$, then $$\varphi(a)\not= a.$$ Prove that $$G$$ is an abelian odd group.

$$\varphi(x)=y\leftrightarrow\varphi(y)=x$$ and I know $$\varphi(e)=e.$$ I can see from this that $$G$$ is a group of odd order. How I prove commutativity? Do you think I can prove first that $$\varphi(a)=a^{-1}$$?
 
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Andrei said:
Here is a problem from some russian book of algebra:$$\varphi(x)=y\leftrightarrow\varphi(y)=x$$ and I know $$\varphi(e)=e.$$ I can see from this that $$G$$ is a group of odd order. How I prove commutativity? Do you think I can prove first that $$\varphi(a)=a^{-1}$$?

as johng's post shows, the answer is yes.
 

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