This is an interesting book! I skimmed some parts and read through his web pages. Seems like most of the value of this book is gathering together and comparing all the various possible definitions of DG concepts. It’s explicitly not a textbook, and I wouldn’t recommend trying to learn from it. The book aims to “fill in the gaps” of all the things usually left out in the usual treatments, but it seems to me you’d want to involve a computer in that–even the author admits that his book will probably never be peer-reviewed.