 The main focus of the Yangists was on the concept of "xing", or human nature, a term later incorporated by Mencius into Confucianism.No documents directly authored by the Yangists have been discovered yet, and all that is known of the school comes from the comments of rival philosophers, specifically in the Chinese texts "Huainanzi", "Lüshi Chunqiu", "Mengzi", and possibly the "Liezi" and "Zhuangzi".The philosopher Mencius claimed that Yangism once rivaled Confucianism and Mohism, although the veracity of this claim remains controversial among sinologists.