Thirty-seven of the forty-two chapters of IFL2 have sets of exercises at the end. So that’s many merry hours to be spent, putting answers to all the exercises online. What joy. And yes, this is pretty time-consuming, to say the least.
But, when taken just a chapter or two at a time, writing up the answers without worrying too much about typographical niceties is quite diverting. And unlike the business of writing the book itself, it is not at all stress-inducing — after all, any slip-ups or silly mistakes or other infelicities can be instantly corrected when noticed, rather than being preserved for ever in embarrassing print.
Here then is the slowly growing page with links to (1) some of the sets of exercises, and then to (2) corresponding sets of answers. Since the exercises are available independently of the book, many of these sets with their answers could eventually be useful to students even if they are not actually using IFL2.
The most recent additions are two sets of questions covering propositional natural deduction proofs for negation and conjunction, and then for disjunction too, with extensive answer sets — talking through strategies for finding the solutions rather in the manner of an examples class. Next up, examples for proofs using the conditional, and more. Watch this space.
Do you have this inference as an exercise:
From ∀xFx ⊃ Gb infer ∃x(Fx ⊃ Gb)
?
It can take a while.
Indeed! In fact, I do the proof in the main text. BUT after I have introduced the following permission: in the middle of a QL derivation, you are allowed to compress PL steps so we can e.g. go from ¬(Fa –> Gb) to Fa and ¬Gb “by PL”. Which speeds things up, and focuses the proof on what currently matters, quantificational reasoning.