@paulgarrett and Dan Romik: in 2014, I wrote an article about bitcoins. This article was accepted in a major brazilian journal of economics. Ever since, I have received a lot of emails like this. In the beginning, I read through them. But now, I just dismiss it as garbage. Two months ago, I received an invitation to write a chapter of an online book about cryptocurrencies. I dismissed it as scam. However, the editor of the book is trustworthy, according to my thesis advisors. Unfortunately, the deadline is very close now. Probably, I am going to miss it. That's the full story.