https://purengom.com/2010/01/08/%eb%a7%8c%ed%99%94-%eb%8b%a8%ed%96%89%eb%b3%b8-%ec%a1%b0%ea%b8%88%eb%a7%8c-%ec%a7%80%eb%82%98%eb%a9%b4-%ea%b5%ac%ed%95%98%ea%b8%b0-%ec%96%b4%eb%a0%b5%ea%b5%ac%eb%82%98/