What a lovely resource! Thank you, author. I just wanted to thank all the authors, especially of textbooks, who put their work online, for free. Their dedicati

What a lovely resource! Thank you, author. I just wanted to thank all the authors, especially of textbooks, who put their work online, for free. Their dedication shows, and how. It is largely due to these free (and free-ish) resources that many people -- including autodidacts and those with limited resources -- are able to further their education. Authors - know that your efforts are very much appreciated!