https://blog.gongquiz.com/2021/03/31/%ec%98%88%ec%9e%a5%ed%86%b5%ed%95%a9-2019-%ec%b4%9d%ed%9a%8c%ea%b3%b5%ea%b3%bc-gpl-plus%ec%a7%80%ed%94%bc%ec%97%98-%ed%94%8c%eb%9f%ac%ec%8a%a4-%ec%98%81%ec%95%84%eb%b6%801-1-5%eb%8b%a8%ec%9b%90/