Solvable group: decomposable in prime order groups?

  • #1
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Main Question or Discussion Point

Hey!

From MathWorld on solvable group:
A solvable group is a group having a normal series such that each normal factor is Abelian. The special case of a solvable finite group is a group whose composition indices are all prime numbers.
But why is that a special case? The way I understand it: the normal series can always be made such that all composition factors are simple, but then the composition factors are both simple and Abelian, and hence (isomorphic to) [itex]\mathbb Z_p[/itex], i.e. the composition index is p (= prime)...
 

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  • #2
fzero
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It is only for a finite group that you are guaranteed to have a composition series. For an infinite group, there may be no normal series where the subgroups are maximal. For instance, ##\mathbb{Z}## cannot have a composition series, since it is not itself simple (every subgroup of ##\mathbb{Z}## is itself isomorphic to ##\mathbb{Z}##).
 
  • #3
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Thank you! I see, so for a finite group the "special case" is always true; that clarifies!
 

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