How to play:
Clicking on one of the buttons reduces that button's number by 1 as well as
those of the four surrounding buttons. Your aim is to set all the buttons to '0'
in as few clicks as possible. You can go back a move and restart a game.
The game levels go from 1, which is very simple, up to 9 which
is fiendishly tricky! There is no regular method of solving but, if you doubt
that a game can be solved, you can hit the emergency 'Solve' button.