https://purengom.com/2011/08/02/%eb%a7%a5%eb%b6%81-as-%ec%84%bc%ed%84%b0%ea%b0%80%ea%b8%b0-%ec%a0%84%ec%97%90-%eb%a7%88%ec%a7%80%eb%a7%89-%ec%88%98%eb%a1%9c%ec%8d%a8/