Forever Undecided

Forever Undecided is the most challenging yet of Raymond Smullyan’s puzzle collections.  It is, at the same time, an introduction—ingenious, instructive, entertaining—to Gödel’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...