Redology (simplified Chinese: 红学; traditional Chinese: 紅學; pinyin: hóng xué) is the academic study of Cao Xueqin's Dream of the Red Chamber, one of the Four Great Classical Novels of China. There are numerous researchers in this field; most can be divided into four general groups. The first group are the commentators, such as Zhou Chun, Xu Fengyi, Chen Yupi, and others. The second group is the index group, which mainly includes Wang Mengruan and Cai Yuanpei.