It's amazing how easy it is to relax when stress is eliminated. Of course, being in such a state can make world problems seem solvable by writing a song; or at least making the effort or showing more interest in finding the truth out. For instance, at the moment, you'd be hard pressed to realise that in the last week there has been an escalation of violence in Iraq, because commercial televisions are dominated by other things.

Why I thought of this was because when a Sudoku problem is too hard, i now walk away from it, and invariably when i come back I will notice something else : for instance, if there's two squares out of three left in a line, and two squares can only be one of two, then you can eliminate both of those from square 3.

And I've got a nice little system going. Here it is : using white- board markers, a $2-shop fridge-sized whiteboard, and a cotton bud (name-change since i bought my present pack!). The given numbers are in black, the possibles in the unsolved squares are red, and the solved but not checked (well i have got a book with the answers in the back so i might as well use them til i stop totally making mistakes) are in blue. So I do a bit, then check them in the book, and if i've got the blue ones right, i make them black. This is also because it's easier visually to just look for black numbers rather than black and blue!!! It is supposed to be fun, after all ;-)

So - in case of not being able to see any more clues - the board can be left like this, or if all the blue were right, turning to black and putting the new correct numbers in the relevant puzzle in the book); or of course if one of the blue ones is wrong, ALL of the blue ones get rubbed out (and it often helps if all the red ones too. By writing the 'knowns' in the book, the puzzle can be rubbed out even if not solved; the ones in the paper are getting harder, so the board is needed for them too (before i got this board set up i nearly went and bought another paper one day because i'd made so much mess of the sudoku i wanted to start again!).

You may have picked up at least two mistakes already in the above puzzle : cosmetically, what's that red 6 doing; and just above the red six in the same column, 4 and 9 can be cotton-budded out, as can the 2 in the same square.... the sort of things that stare you straight in the face after a break.

It wasn't long at all until the whole puzzle was out : here it is solved, still with the blue numbers.

I notice online the sudoku pages don't mention whiteboards; just why computer programs are the better way to do sudoku. I'd rather this one, as you can't cheat : the rule is if one blue number is wrong, all blue are erased. Also it's easier staring at a piece of paper than an illuminated computer screen. I've still got to find if this is the 'magic square' of maths textbooks - some page mentioned it is Euclid. On first (googled) glance it's not exactly the same, but interestingly enough,the next googled glance attributed the knowledge of magic squares to chinese, japanese and tibetan mathematicians and philosophers, citing the use of number theory in the I-Ching.