Nerdy annoyance

Lost a number of hours, too many, on a mysterious LaTeX problem. It turns out that fitch.sty (useful for setting Fitch-style proofs) loads a package mdwtab.sty which isn’t fully compatible with the standard tabular environment (useful for setting truth-tables). So when I added  fitch.sty to the preamble to the book source, a few truth-tables mysteriously lost horizontal lines. Took me longer than it should have done to find the culprit. Warning now added to the page on natural deduction packages in LaTeX for Logicians.

Right: back to thinking a bit about how I want to handle empty domains later …