Sudoku puzzles are highly addictive because the instructions are unchanging regardless of the degree of difficulty.
For this set, however, expect to work on hard to extra hard challenges.
Remember that Sudoku does not come with clues so you really have to figure out the answers on your own.
Of course, there's no rule saying you can't ask help.
You definitely can.
Evil sudoku puzzle books hard to extra hard challenges, paperback/Senor Sudoku
