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Let $G$ be a finite group and $H,K$ be subgroups of $G$ such that $H$ is normal in $K$ and $K$ is characteristic in $G$. Is $H$ normal in $G$?

I know that if $H$ is characteristic in $K$ and $K$ is normal in $G$, then $H$ is normal in $G$. However, I was wondering if the above statement is true as well.

Shaun
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Guest
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1 Answers1

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Not always. For a counterexample let $G=A_4$ and let $K$ be its Sylow $2$-subgroup. The Sylow $2$-subgroup is unique, so it is characteristic. In this case $K$ is abelian, so $H\le K$ implies $H\unlhd K$. But if $H$ is cyclic of order two, it is not a normal subgroup of $G$.

Jyrki Lahtonen
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