You could ask the author "wardfarnsworth at gmail.com". I have been in touch with him before about his chess website https://www.chesstactics.org https://www.ch

You could ask the author "wardfarnsworth at gmail.com". I have been in touch with him before about his chess website https://www.chesstactics.org https://www.chesstactics.org based on his book "Predator at the Chess board". He was quite responsive.