https://blog.wongcw.com/2021/10/12/%e7%a0%94%e7%a9%b6%ef%bc%9a%e8%88%87%e5%8e%9f%e5%a7%8b%e6%af%92%e6%a0%aa%e7%9b%b8%e6%af%94-delta%e8%ae%8a%e9%ab%94%e4%bd%bf%e6%82%a3%e8%80%85%e7%9a%84%e6%ad%bb%e4%ba%a1%e9%a2%a8%e9%9a%aa%e5%a2%9e/