We are keeping our social distance, ducking out of meetings, avoiding cafés, having at least some food supplies delivered rather than going to the shops, and so on — all in all, erring on the side of caution, given age considerations. Keep calm and carry on. What else can you do?
So I’ve had a bit more time than expected to plough on with getting answers to IFL2 exercises online (discovering along the way that one of the exercises asked students to prove a falsehood — I live and learn: fortunately I can still change the final final PDF for the book).
By my lights, the key thing for philosophy students is to understand the principles behind a natural deduction system (and ideally, to get some sense of what are the deep ideas, and what are matters of presentational choice). Doing a few exercises no doubt helps understanding. Getting expert at proof-discovery goes beyond what is really necessary. Still, I can’t resist: I have now provided very extensive worked answers — over forty pages — with a lot of hints and tips for proof discovery. You will find the exercises and answers here. I hope they will be of some interest even to those not using IFL2 (e.g. users of forall x).
Exercises for QL natural deduction next … is there no end to the fun?