https://purengom.com/2010/07/28/%ec%83%88%eb%a1%9c%ec%9a%b4-%ec%95%84%ec%9d%b4%eb%a7%a5%ec%9d%84-%eb%b3%b4%eb%8b%88-%eb%8b%b9%ed%96%88%eb%8b%a4%eb%8a%94-%eb%8a%90%eb%82%8c%ec%9d%b4-%eb%93%9c%eb%8a%94%ea%b5%b0%ec%9a%94%ec%83%88/