KenDoku, Volume 1: 100 Puzzles to Build Your BrainPaperback, 17 February 2009

The puzzles, either 6 x 6 or 9 x 9, look like Killer Sudoku games, but in addition to numbers, players also contend with math operators (+ - × ÷) within "fences" on the puzzle. Players reach the total at the top left of the fenced area by using the operator on all the numbers within it. Although the solution is a valid Sudoku solution, 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.