The Home of Perfect Sudoku and other puzzles

Concerning the training of the brain it was 4 years ago stated in the Danish engineering news that research had found that Sudoku is the best training for the brain. Later there has come another “game” that should be a little bit better for the brain. I’ve now been solving Sudokus for 5 year, but first 4 years ago, after reading the engineering, I started buying Sudoku books. Normally, nearly each afternoon, I get some time for relaxing on Sudoku, if I don’t have mathematical or programming problems to solve, which I like the most. During the years I’ve bought 20 books with Suduko, and some of them I’ve been through 2 times, with a couple of years between. And these books, all bought by my own research in Amazon, as none of the persons I know solve Sudokus, and thereby being able to advise me which books to buy, and being easy or difficult. And of the books, all previous being the size 9*9, I mostly like those by Will Shortz, but probably there are others I will like more, that are for being more difficult. But in my search after more difficult Sudokus I found a few books with these 5 double 9*9 Sudoku and the immediately 2 month ago ordered the actual book 2. And I must say that I like it very much, and when I’ve finished this book I without doubt will order the next of these DJAPE. Until now I’ve solved half of the 101 in this book, and have used at least 2 hours on each one. First after each time, in the PC, by the use of Excel, having made a copy of the actual one and then with yellow color at the known numbers.