Exciting headline news. Like the Gödel book, IFL2 is now available as a freely downloadable PDF. There is also an inexpensive Amazon print-on-demand book, for those who want a hard copy. UK link; US link. (Find on your local Amazon by using the ASIN identifier B08GB4BDPG in their search field.)
My apologies to anyone who bought the book at full price recently; but it was a surprise to me too that new publication arrangements became possible. Since I’m more interested in spreading the logical word than in totting up a few royalties (authors of logic books stand to make a fortune, of course …), I’ve decided to give the book away, or to provide access to a hard copy within a few pennies of the allowed Amazon minimum price. It’s a quite rotten time for students; so giving free/cheap access to decent learning materials when we can seems especially appropriate now. (Anyone thinking of using the book as a course text can be assured it will remain free.)
As I said about the Gödel book, the print-on-demand version is very decently printed, at least by Amazon’s UK printer, but the cover isn’t as good as a trade paperback’s (I don’t just mean the design, but the way it lies), and the binding is a bit tight. But on the other hand, it is a third of the price of the original, so I don’t suppose anyone will complain too loudly.
A reminder: The first edition of IFL concentrated on logic by trees. Many looking for a course text complained about this. The second edition, as well as significantly revising all the other chapters, replaces the chapters on trees with chapters on a natural deduction proof system, done Fitch-style. Which again won’t please everyone! So the chapters on trees are still available, in a revised form, here on the website. But it was considerations of space in the printed version that led to the relegation of (versions of) those chapters to the status of online supplements. This was always a second-best solution. Ideally, I would have liked to have covered both trees and natural deduction (while carefully arranging things so that the reader who only wanted to explore one of these still has a coherent path through the book). With e-publication, the question of length isn’t so vital. So over the coming months, I may be inclined to revert to the inclusive plan, and so eventually produce a third edition. We’ll see. IFL3 is for the future. For the moment, enjoy the delights of IFL2!