https://purengom.com/2008/09/08/%ed%98%84%eb%8c%80%ed%83%9d%eb%b0%b0-%eb%b0%9c%ec%86%a1-%ec%82%ac%ec%a0%88%ed%95%a9%eb%8b%88%eb%8b%a4-%eb%8f%84%ea%b8%89%ea%b3%bc-%ec%9e%ac%ed%95%98%eb%8f%84%ea%b8%89%ec%9d%98-%ed%8f%90%ed%95%b4/