https://purengom.com/2008/04/09/%ed%91%b8%eb%a5%b8%ea%b3%b0-%eb%98%90%eb%af%b8-%ec%9d%b4%ec%95%bc%ea%b8%b0-3-%eb%82%98%eb%8a%94-%eb%aa%87%ec%82%b4%ec%9d%b4%eb%82%98-%ec%82%b4-%ec%88%98-%ec%9e%88%ec%9d%84%ea%b9%8c/