Will Shortz Presents Difficult Sudoku: 200 Hard Puzzles

Are you tough enough?
Take on this collection of 200 difficult sudoku puzzles and find out!

Includes:
-200 hard puzzles
-Perfect portable size
-Edited by Will Shortz

Also in the series:
-Will Shortz Presents Daring Sudoku
-Will Shortz Presents Dangerous Sudoku