https://www.syu.ac.kr/blog/%ec%b2%ad%eb%85%84-%ec%b7%a8%ec%97%85-%ec%95%84%ec%b9%b4%eb%8d%b0%eb%af%b8_%eb%b9%85%eb%8d%b0%ec%9d%b4%ed%84%b0-%eb%b6%84%ec%84%9d%ec%9d%84-%ed%99%9c%ec%9a%a9%ed%95%9c-%eb%8d%b0%ec%9d%b4%ed%84%b0/%ec%8a%ac%eb%9d%bc%ec%9d%b4%eb%93%9c7-8/