13 Easy Ways to Solve Hard Sudoku Puzzles - wikiHow
100 Free Printable Sudoku Puzzles
Extremely difficult sudoku puzzles: for smart people only . solution at the end of the book.: publishers, Brain river: 9798590828975: Amazon.com: Books
Hard Sudoku level 3 Game 13: Step by Step Easy Solution
Samurai Sudoku Puzzle Book for Adults - Hard: 500 Difficult Sudoku Puzzles Overlapping into 100 Samurai Style (Paperback) | Malaprop's Bookstore/Cafe