Naive Lie Theory
《Naive Lie Theory》 · 第 177 页 · Chapter 10，Section 10.1.4「Exercises」，Exercise 2
Take $G = \mathrm{SO}_n$ ($n \ge 5$, characteristic $\ne 2$). Show that $G$ is not simply connected. The group $\widetilde G$ of the preceding exercise is the spin group $\mathrm{Spin}_n$.