Observer killer sudoku | Life and style | The Guardian
Killer Sudoku Archives - The Art of Puzzles | The Art of Puzzles
Sumdoku Puzzles: 300 Sum-Doku (Also Know As Killer Sudoku) Puzzles. 100 Easy, 100 Medium And 100 Hard. Solutions At The Back Of The Boo (Paperback) | RJ Julia Booksellers