Killer sudoku

Telegraph Killer Sudoku 1

Telegraph: Killer Sudoku 2

The Guardian Killer Sudoku 2

Overworked & Underpuzzled: Killer Sudoku

The Guardian Killer Sudoku 1

Mensa Killer Sudoku

Djape: Revenge of Killer Sudoku

Killer Sudoku, Book 2: 200 Mind-bending Puzzles (Killer Sudoku, 200 puzzles for all standards)

The Telegraph: Killer Sudoku 2 (the Telegraph Puzzle Book

Mensa Killer Sudoku: More than 200 of the most difficult number puzzles