arXiv · 1202.5736
Let $K$ be a subgroup of a finite group $G$, and suppose that $G=KN_G(P)$ for every Sylow subgroup $P$ of $K$. Then the subgroup $K$ is normal in $G$.
V. S. Monakhov. 2012-02-26. On the Frattini lemma. https://arxiv.org/abs/1202.5736
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