https://www.syu.ac.kr/blog/%ec%b2%ad%eb%85%84%ec%9d%b8%ec%9e%ac-%ec%96%91%ec%84%b1-%ed%94%84%eb%a1%9c%ea%b7%b8%eb%9e%a8-%eb%aa%a8%ec%a7%91-%ea%b3%b5%ec%a7%80/%eb%b6%99%ec%9e%843-%ea%b0%9c%ec%9d%b8%ec%a0%95%eb%b3%b4-%ec%88%98%ec%a7%91-%eb%b0%8f-%ec%9d%b4%ec%9a%a9-%eb%8f%99%ec%9d%98%ec%84%9c-2/