https://www.syu.ac.kr/blog/%eb%85%b8%ec%9b%90%ea%b5%ac-%ec%b2%ad%eb%85%84%ec%9d%bc%ec%9e%90%eb%a6%ac%ec%84%bc%ed%84%b0-%ec%b2%ad%eb%85%84%eb%82%b4%ec%9d%bc-%ea%b0%9c%ea%b4%80-%eb%b0%8f-%ec%9d%b4%ec%9a%a9-%ec%95%88%eb%82%b4/%eb%85%b8%ec%9b%90-%ec%b2%ad%eb%85%84%eb%82%b4%ec%9d%bc-%ec%9c%84%ec%b9%98%eb%8f%84%ea%b3%b5%eb%ac%b8%ec%b2%a8%eb%b6%80%ec%9a%a9-2/