Sorry Everyone, No Update Today

I have been sitting in front of the computer for a whole day, writing, deleting, and writing. I really didn’t write something that I am satisfied with. In the end, there is only this part left. I don’t want to scribble every word, but the state is a bit behind me. I should revise it several times. If the last part is not well written, the evaluation of the whole book will be lowered!