https://blog.wongcw.com/2018/11/27/rms-%e6%89%b9%e8%a9%95%e6%af%94%e7%89%b9%e5%b9%a3%e5%8a%9b%e6%8e%a8%e6%9b%bf%e4%bb%a3gnu-taler/