https://blog.wongcw.com/2021/03/28/%e7%b4%85%e5%b8%bd%e7%99%bc%e5%b8%83richard-stallman%e9%87%8d%e8%bf%94fsf%e8%91%a3%e4%ba%8b%e6%9c%83%e7%9b%b8%e9%97%9c%e8%81%b2%e6%98%8e/