Mr. Feng Youlan wrote a congratulatory message to 1984 Zhouyi forum: "Zhouyi philosophy can be called cosmic algebra. Algebra is a branch of arithmetic, but there are no numbers in it, just some formulas, which are represented by some symbols. For numbers, these formulas are just empty sets. Because they are empty sets, you can insert any number. That's what I mean when I say Zhouyi can be called cosmic algebra. The Book of Changes itself doesn't talk about the specific universe, just some empty sets, but everything can be put in. This is called' God has no way, and it is easy to die'. "