1, science. This time, many mistakes were corrected, and we tried our best to be "rigorous" and "accurate", and not a single scientific mistake could be made. I hope I can "flip through the Chinese Mathematical Olympics textbook" as the reader said, and that set of books is accurate.

2. readability. This revision has deleted some topics that are too difficult and too much beyond the actual level (such as the arrangement and combination formula of the fourth grade), and the text is as concise as possible.

3. The textbook used in Chinese mathematics course is "Renhua School Olympiad", which is the most systematic and longest-used textbook.