Frank Longo

Absolutely Nasty Sudoku: Even Nastier - Level 1

Absolutely Nasty Sudoku: Even Nastier - Level 2

Absolutely Nasty Sudoku: Even Nastier - Level 3

Absolutely Nasty Sudoku: Even Nastier - Level 4

Absolutely Nasty Sudoku Level 2

Absolutely Nasty Sudoku Level 3

Skill Builder Sudoku: Easy to Medium

Skill Builder Sudoku: Hard to Expert

Skill Builder Sudoku: Medium to Hard

Great Book of Sudoku

Pause for Puzzles: Sudoku for Mindfulness

Sudoku Puzzles for the Weekend

Blockbuster Book of Sudoku

Way Beyond Black Belt Sudoku

mental_floss Sudoku

Extreme Sudoku

Samurai Sudoku Challenge

Puzzlewright Guide to Solving Sudoku

The Nastiest Sudoku Book Ever

Beyond Black Belt Sudoku