https://purengom.com/2007/12/21/%ec%95%84%ec%9d%b4%eb%a7%a5%ec%9d%98-%ed%99%94%eb%a9%b4-%eb%aa%a8%ed%89%81%ec%9d%b4-%ea%b2%80%ea%b2%8c-%eb%b3%80%ed%95%98%eb%8a%94-%ed%98%84%ec%83%81-%ec%b2%b4%ed%81%ac%ed%95%98%ec%84%b8%ec%9a%94/