I'm pretty bummed that this submission is in HN purgatory for some reason, but it's really great to read these nice comments! I'm glad y'all have found the book useful and enjoyable :)
It set off the voting ring detector.
We'll reduce the penalty, since the post is probably of interest to the community.
Edit: we also put "Show HN" in the title, since it's your book, it's available to read, and it's a major piece of work.