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. The third group are the textual critics, including Hu Shi and Yu Pingbo. The final group are the literary critics. There are various researchers in this group, most notably Zhou Ruchang.