|This collection of puzzles has a particular audience in mind.
It's for those who don't bother doing sudoku puzzles from
newspapers or magazines because they're too easy. Even most
sudoku books these days don't have challenging puzzles even in sections
called "evil" or "diabolical".
Then there are the worlds hardest puzzles. Those are so difficult that you need a computer program to solve them. You won't find those puzzles here.
The puzzles in this collection are designed for the puzzle solvers who still enjoy working puzzle using paper and pencil. These puzzles can be exported in popular formats to use in solvers as well.
These puzzles cannot be solved using just the traditional solving techniques. You're going to need to understand X-wings, XY-wings, W-wings, X-chains, Colors, Unique Corners, etc. Check out my tutorial for information on any of these.
But you're not going to need to resort to brute force for a solution either.
I guarantee that all of these puzzles are valid (one unique solution only).
I am by no means the leading sudoku authority. I just like creating challenging puzzles and sharing them. I welcome your commments, suggestions, criticisms at firstname.lastname@example.org.