What book does the yen come from?

The book written by Yan heavenly stems and earthly branches Universiade is Zhouyi. Zhouyi is the most important book in China's ancient divination, which contains many contents related to heavenly stems and earthly branches. In the Book of Changes, heavenly stems and earthly branches was mainly used to explain the law of the generation and change of all things in the universe, and later gradually applied to numerology, divination and geomantic omen.