When you were in NTUC, you produced the book Logic 9. I find them to be quite fun to use, especially for me to try the game when I travel. Where can I buy the book?
It is now out of stock. Most people now play Sudoku (which is the commonly known name of the game) on their mobile device. So the Logic 9 booklet is just history.
If you like to learn the skill of playing the game, here is an e-book that gives you the tips on how to be a Sudoku expert. And it is easy to follow. No difficult mathematics. Just simple daily practice. And enjoy.
This is a useful pastime for elderly people to keep their mind alert and free from dementia. And they can choose a simple level - and really enjoy the game.