Top solvers can try their hand at the One-Sided Gordonian Rectangle; Extended Gordonian Rectangle; Gordonian Polygon; and Alternating Digits. (But they can take comfort in knowing that no more than one will occur in any single puzzle.)

Sudoku designers the world over will weep and gnash their teeth at the revelations in this comprehensive guide to cracking the addictive puzzles--but solvers will find it absolutely invaluable as they seek to improve their skills. Even experts don't know all these tricks: hidden pairs, naked pairs, X-wings, jellyfish, squirmbag, bivalue and bilocation graphs, and chains, plus the exclusive Gordonian logic methods that turn the toughest puzzles into a breeze. There are hundreds of sudoku to practice on. A special addition is a reprint of the very first sudoku ever published!

Sudoku super-master Frank Longo and mental_floss, the magazine for trivia lovers, bring fans a collection of superb puzzles sure to stimulate the brain. Longo's puzzles are always top-notch, and because these increase in difficulty as the book goes along, they're perfect for helping solvers build their skills.