These logic puzzles provide entertaining variations on Gödel's incompleteness theorems, offering ingenious challenges related to infinity, truth and provability, undecidability, and other concepts. No background in formal logic necessary.

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 exercises and adventures—including journeys into the “other possible worlds” of Kripke semantics—even the most illogical of us come to understand Gödel’s two great theorems on incompleteness and undecidability, some of their philosophical and mathematical implications, and why we, like Gödel himself, must remain Forever Undecided!

Characters from Alice's Adventures in Wonderland and Through the Looking-Glass populate these 88 intriguing puzzles. Mathematician Raymond Smullyan re-creates the spirit of Lewis Carroll's writings in puzzles involving word play, logic and metalogic, and philosophical paradoxes. Challenges range from easy to difficult and include solutions, plus 60 charming illustrations. "An ingenious book." — Boston Globe.

In his new book, Raymond Smullyan, grand vizier of the logic puzzle, joins Scheherazade, a charming young woman of “fantastic logical ingenuity,” to give us 1001 hours of brain-teasing fun. Scheherazade, we find, has gotten back into hot water with the king, and is once more in danger of losing her head at down. But, thinking quickly, she tempts the king to stay her execution by posing him the most delightfully devious mathematical and logic puzzle ever invented. They keep him guessing for many more nights until the fatal hour has passed, and she keeps her head. The Riddle of Scheherazade includes several wonderful old chestnuts and many fiendishly original puzzles, 225 in all. There are logic tricks and number games, metapuzzles (puzzles about puzzles), liar/truth-teller exercises, Gödelian brian twisters, baffling paradoxes, and an excursion, under Scheherazade’s expert guidance, into an amusing new field invented by Smullyan, called “coercive” logic, in which the answer to a problem can actually change the fate of the puzzler! An absolute must for all puzzle fans—from the middle-school whiz to the sophisticated mathematician or computer scientist.

The author of Forever Undecided, Raymond Smullyan continues to delight and astonish us with his gift for making available, in the thoroughly pleasurable form of puzzles, some of the most important mathematical thinking of our time.

Kurt Godel, the greatest logician of our time, startled the world of mathematics in 1931 with his Theorem of Undecidability, which showed that some statements in mathematics are inherently "undecidable." His work on the completeness of logic, the incompleteness of number theory, and the consistency of the axiom of choice and the continuum theory brought him further worldwide fame. In this introductory volume, Raymond Smullyan, himself a well-known logician, guides the reader through the fascinating world of Godel's incompleteness theorems. The level of presentation is suitable for anyone with a basic acquaintance with mathematical logic. As a clear, concise introduction to a difficult but essential subject, the book will appeal to mathematicians, philosophers, and computer scientists.

This fanciful, original collection for readers of all ages features arithmetic puzzles, logic problems related to crime detection, and logic and arithmetic puzzles involving King Arthur and his Dogs of the Round Table.