Book excerpt: Hot on the heels of the first two volumes,Kendoku: Extremeshows that when it comes to mind-bendingly difficult logic/arithmetic puzzles, too much is never enough! Combining the logic of Sudoku with the math play of KenKen, Kendoku’s rules are simple enough: The puzzles, either 6x6 or 9x9, look like Killer Sudoku games but in addition to numbers, players also must contend with math operators (+ - × ÷) within "fences” on the puzzle. The total at the top left of the fenced area is arrived at by using the operator on all the numbers within the fenced area. The solution is a valid Sudoku solution. But unlike in Killer Sudoku, in Kendoku numbers are allowed to be repeated within a fenced area as long as the result doesn't break the rules for a valid Sudoku.