https://blog.gongquiz.com/2023/01/26/%eb%b6%88bool-%eb%8c%80%ec%88%98%ec%9d%98-%ec%a0%95%eb%a6%ac%eb%a5%bc-%eb%82%98%ed%83%80%eb%82%b8-%ea%b4%80%ea%b3%84%ec%8b%9d-%ec%a4%91-%ed%8b%80%eb%a6%b0-%ea%b2%83%ec%9d%80-%ec%82%b0%ec%97%85/