https://purengom.com/2008/11/06/%eb%a3%a8%ec%9d%b4%eb%b9%84%ed%86%b5-%ec%a7%80%ea%b0%91%ec%9d%84-%ec%82%ac%eb%b3%bc%ea%b9%8c-%ed%95%98%eb%8b%a4%ea%b0%80-%ea%b0%80%ec%a7%9c-%eb%aa%85%ed%92%88-%ea%b7%b8%eb%a6%ac%ea%b3%a0-%ec%a7%84/