Truth trees for propositional logic

I’ve revised (and of course revised again, and re-revised!) the chapters on truth-trees for propositional logic for the second edition of my intro logic text. What took four chapters and forty pages has now become two chapters and twenty-eight pages, with exercises still to be added.

I previously went from T/F-signed trees to T-signed trees to unsigned trees in a messy way, and that’s gone (so we now have just one sort of tree, initially T-signed and then the Ts are dropped). I previously did trees first for the connectives and/or/not and then added the material conditional and biconditional in a separate chapter; now I just treat the first four connectives in one chapter and the biconditional is relegated to exercises. There are other tidyings, and I’ve dropped the stuff about saturated sets (destined to become an online extra).

So I hope the result reads more cleanly and (even) more accessibly. Here it is. All comments most gratefully received!