Instruct: Classify the given Amazon review into positive or negative sentiment.
Query: World class book.

Totally excellent book. I had checked it out of university libraries several times over the years, and was astounded that I could buy a copy for a few bucks. I turned out to be a university library cull. What in the world is up with that?In all differential equation courses, one spends a day or two dealing with what to do if the right hand side is not zero, i.e., there is a forcing function. This book is a well organized exposition of what you get when you follow up on the standard methods (variation of constants, etc.). The details are worked out for the standard DE's of Math Physics and basic forcing functions. The new functions arising are analyzed.It is a great guide to manipulating power series in nontrivial situations. You will discover why Gauss set up the hypergeometric function the way it is.