Redology (simplified Chinese: ; traditional Chinese: ; pinyin: ) 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. The third group are the textual critics, including Hu Shih and Yu Pingbo. The final group are the literary critics, including Zhou Ruchang and Li Xifan.