Getting a little bored with easy sudokus? Or fed up with sudokus that require you to guess the solution? Or sudokus that have more than one solution? Or sudokus of which the degree of difficulty is given in very inflated terms like excruciating or extreme? In this book we have none of that. We have proper difficult sudokus with only one solution, that can be solved by direct reasoning. It is just that you need to know a number of techniques because they really are rather difficult. Just to make sure that you will not fail because you do not know all techniques involved, we explain first all techniques that have been used for the construction of these sudokus. If you think that this is like giving away the solutions you are quite mistaken. Even when you know all these techniques the sudokus are difficult. You will have to use many of them just to solve a single sudoku. Which ones and in which order is up to you. Each sudoku should keep you busy for at least an hour, probably much more, although it is of course possible that you are one of the very few who can do it faster. I am not one of those. It gives me a sense of achievement each time I solve one.