习题 5, § 2

令$G$为连通拓扑群，并令$H$为$G$的紧致法线子群，且不存在任意小的子群（章III, § 2，习题30）。 Show that $H$ is contained in 中心 of $G$. (Observe that for $s$ close to $e$ in $G$, 像 of $H$ under $x \to sx s^{-1}$ is arbitrarily close to $e$.)