think of this as being a stronger type of normality. Prove that a characteristic subgroup is normal and give a counterexample to show that a normal subgroup need not be characteristic.

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4. A subgroup is called characteristic if it is invariant under all automorphisms.
We write H char G if 0(h) € H for all h H and 0 € Aut(G). We may
think of this as being a stronger type of normality. Prove that a characteristic
subgroup is normal and give a counterexample to show that a normal subgroup
need not be characteristic.
Hint: In an abelian group all subgroups are normal. Are they call characteris-
tic?
Transcribed Image Text:4. A subgroup is called characteristic if it is invariant under all automorphisms. We write H char G if 0(h) € H for all h H and 0 € Aut(G). We may think of this as being a stronger type of normality. Prove that a characteristic subgroup is normal and give a counterexample to show that a normal subgroup need not be characteristic. Hint: In an abelian group all subgroups are normal. Are they call characteris- tic?
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