Maximal subgroup normalizer criterion
= Maximal subgroup normalizer criterion
{title2=$M=N_G(N)$}
For a maximal subgroup $M$ of a finite nonabelian simple group, take a minimal nontrivial normal subgroup $N$ of $M$. It is a <characteristically simple group>. Its normalizer contains $M$ but cannot be the whole simple group, since $1<N\le M<G$. Maximality gives equality.