Hi Dan Wu. Even though I did not understand the words that you are using, maybe you are using a different or unreliable translation, I understand the thought of the whole article. This is very informative, considering the fees that are being used in every single transaction. I was very interested when I saw the title of your post, therefore I went and read the article and all the previous article. This specific article makes me more interested. This makes everyone informed of the concept known as double spending, and providing knowledge about public and private key pair. Continue to provide knowledge about the whole platform and inspire others. You are doing great.