Note
Today, in my garage, I discovered a booklet entitled "O-DOKU." I have never seen this booklet before.
The inside cover:
"Congratulations! You are now the proud owner of the first ever O-doku book to be published.
O-doku's history started in august [sic] 2005. During the World Championships in Japan members of the Danish national team changed the numbers of a sudoku to control description symbols and the first O-doku was born. Since then others have done the same and O-doku's have appeared in several magazines and on the internet."
The back cover:
"WARNING!
This book contains time-consuming and addictive material. There will be no turning back - once started you will be hooked, but it is fun to solve O-doku! Some might call you a nerd as you work through this book, but remember - you are just an enthusiast."
Well, then.