Why do there seem to be so many forks of this book, like:<p><a href="https://openlogicproject.org/2017/01/18/forall-x-calgary-remix/" rel="nofollow">https://openlogicproject.org/2017/01/18/forall-x-calgary-rem...</a>
I used this book to teach an introduction to logic class. The students certainly appreciated not having to pay >$100 for a text book that they wouldn't read.
Logic is my favourite branch of maths. It still boggles my brain to think that the fearsome complexity of computing today ultimately boils down to True, False and a handful of logical connectives (conjunction, disjunction, negation).