High quality work that helps bridge the gap between upper division and lower division math. Well priced because the author believes math textbooks are overpriced and tries to bring more equity into the math field. I highly recommend buying this book if you are new to proof writing and taking upper divisions soon. It expands on topics in discrete math and other subjects like pigeonhole principle etc. I bought this book out of curiousity and think it is a killer deal. I support this author’s genuine intentions and hope you enjoyed the book as much as I did