Can a Finite Group Acting on a Set Have No Fixed Points?

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SUMMARY

A finite group \( G \) acting transitively on a finite set \( X \) with more than one element must have at least one element that is free of fixed points. This conclusion is established through the properties of group actions and the definition of transitivity. The problem was successfully solved by forum members castor28 and Olinguito, demonstrating the application of group theory concepts in finite groups.

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  • Understanding of finite group theory
  • Familiarity with group actions and transitivity
  • Knowledge of fixed points in mathematical contexts
  • Basic concepts of set theory
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  • Study the properties of transitive group actions in detail
  • Explore examples of finite groups and their actions on sets
  • Learn about fixed point theorems in group theory
  • Investigate the implications of group actions in combinatorial settings
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Euge
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Here is this week's POTW:

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Let $X$ be a finite set with more than one element, and $G$ be a finite group acting transitively on $X$. Show that some element of $G$ is free of fixed points.

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Remember to read the https://mathhelpboards.com/showthread.php?772-Problem-of-the-Week-%28POTW%29-Procedure-and-Guidelines to find out how to https://mathhelpboards.com/forms.php?do=form&fid=2!
 
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This week's problem was solved correctly by castor28 and Olinguito. You can read castor28's solution below.
Let $|X|=n>1$. As the action is transitive, there is only one orbit. By Burnside's lemma, this is equal to the average number of points fixed by an element of $G$.
The identity of $G$ fixes all the $n$ points. If every element of $G$ fixed at least one point, the average would be grater than $1$.
 

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