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.

These recreational logic puzzles provide entertaining variations on Gödel's incompleteness theorems, offering ingenious challenges related to infinity, truth and provability, undecidability, and other concepts. Written by a distinguished mathematician and creator of numerous popular puzzle books, this volume requires no background in formal logic and will delight readers of all ages.

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!

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.

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.

More than two hundred new and challenging logic puzzles—the simplest brainteaser to the most complex paradoxes in contemporary mathematical thinking—from our topmost puzzlemaster (“the most entertaining logician who ever lived,” Martin Gardner has called him). Our guide to the puzzles is the Sorcerer, who resides on the Island of Knights and Knaves, where knights always tell the truth and knaves always lie, and he introduces us to the amazing magic—logic—that enables to discover which inhabitants are which. Then, in a picaresque adventure in logic, he takes us to the planet Og, to the Island of Partial Silence, and to a land where metallic robots wearing strings of capital letters are noisily duplicating and dismantling themselves and others. The reader’s job is to figure out how it all works. Finally, we accompany the Sorcerer on an alluring tour of Infinity which includes George Cantor’s amazing mathematical insights. The tour (and the book) ends with Satan devising a diabolical puzzle for one of Cantor’s prize students—who outwits him! In sum: a devilish magician’s cornucopia of puzzles—a delight for every age and level of ability.

Fun for the whole family, the book contains more than 100 superb puzzles. Merlin the Magician, Avalon, King Arthur, and other mythical people and places feature prominently.