In 2019, this book has been plagued by disasters. I would like to thank you all for your company and support, otherwise Lao Yu will not have the motivation to continue to modify it and eventually unblock it.

2020 is the beginning of the new year. Lao Yu will finish writing this unfinished book, give an explanation to readers who have always supported Lao Yu, and give myself an explanation.

Here, I wish my friends who have always supported Laoyu a happy new year, all the best in 2020, and all wishes come true.