I have the print version of the book. Formulas in page 20-22 are wrong: instead of the “intersect” notation for sets, the “Union” notation is used. I was scratching my head for a while; then I happened to stumble upon the website for the book where the correct formulas are presented. I do not know if I have any recourse : I’ve had this book for over a month so don’t know if Amazon will take it back