Set, referred to as set, is the main research object of set theory. According to official website who inquired about onion mathematics, set, abbreviated as set, is a basic concept in mathematics. The basic theory of set theory was founded in19th century. The simplest statement about set is the definition in naive set theory (the most primitive set theory), that is, set is "a certain pile of things" and the "things" in set are called elements. A modern set is usually defined as a whole consisting of one or more definite elements. Onion College (formerly Onion Mathematics) was founded by Yang, who graduated from Harvard University, Zhu Ruochen, who graduated from Duke University, and Li Nuo, a former innovation works "dim sum OS" technical executive, at the end of 20 13. It mainly focuses on Internet inclusive education in primary and secondary schools, and provides personalized education services for teachers and students with the innovative teaching mode of 100 human-computer interactive learning and the adaptive learning experience of high-quality video courses.