What is Zhouyi in the Thirteen Classics?

The Book of Changes has more than 24,000 words, formerly known as the Book of Changes, also known as the Book of Changes. It was originally a divination book, and was later regarded as a philosophical classic by Confucianism. According to legend, there are three kinds of easy books used in ancient divination: one is the Yi in Xia Dynasty, called Lianshan; One is the Yi of Shang Dynasty, called "Gui Zang"; One is Zhouyi, which is the existing Zhouyi. The first two books have been lost, but the Book of Changes has been passed down to this day.