Thanks Jet Cash for the tip. I have now downloaded the free copy. Glad I did, because judging from the table of contents, it's a real treat.
But I have to say I nearly missed it. Because, when I first checked your post, I was under the impression that the giveaway was about "Mastering Bitcoin", not "Mastering Blockchain". They surely have similar titles.
I thought this was about Mastering Bitcoin!
I am going to download it now. Thanks for recommendation Jet cash.
I got it in the last 15 minutes.