the 1980s had been rejected and now some of it has come back so that stuff that's really stood the test of time is what I focused on putting into the book there's also I guess two different philosophies about how you might write a book one philosophy is you try to write a reference that covers everything and the other philosophy is you try to provide a high level summary that gives people the language to understand a field and tells them what the most important concepts are the first deep learning book that I