The ultimate Sudoku challenge: 200 of the most challenging puzzles 
Hamlyn 
 - New York  Research Press  2005 
 - 190 p 
<br/><br/><label>ISBN: </label>9780600614852 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Puzzles
<br/><br/><label>Dewey Class. No.: </label>793.74 HAM