Forever Undecided is the most challenging yet of Raymond Smullyan's puzzle collections. It is, at the same time, an introductioningenious, instructive, entertainingto Gdel's famous theorems. With all the wit and charm that have delighted readers of his previous books, Smullyan transports us once again to that magical island where knights always tell the truth and knaves always lie. Here we meet a new and amazing array of characters, visitors to the island, seeking to determine the natives' identities. Among them: the census-taker McGregor; a philosophical-logician in search of his flighty bird-wife, Oona; and a regiment of Reasoners (timid ones, normal ones, conceited, modest, and peculiar ones) armed with the rules of propositional logic (if X is true, then so is Y). By following the Reasoners through brain-tingling exercises and adventuresincluding journeys into the ';other possible worlds' of Kripke semanticseven the most illogical of us come to understand Gdel's two great theorems on incompleteness and undecidability, some of their philosophical and mathematical implications, and why we, like Gdel himself, must remain Forever Undecided!