On 26-Jan-09 9:39, scott wrote:
>>  If trial-and-error was acceptable in a sudoku, then you could just as
>> well give an empty sudoku grid for someone to solve.
> 
> I was assuming (as do most others I think) that sudoku problems only 
> have 1 unique solution.  What would be the point of an empty grid?
> 
>>  The principle in sudoku puzzles is that they can be solved without 
>> having
>> to guess anything. The chain of required deductions may go very deep in
>> the hardest sudokus, but it's always possible to solve it without having
>> to guess.
> 
> However most people would rather use trial and error than go very deep 
> in logical deductions.  ie write a 3 in lightly and fill in a few more 
> squares based on that, oops no that doesn't work, original square must 
> have been a 6 then.  

You can do the simple ones by trial and error but that would take too 
much time for the more difficult ones. There you need deduction to 
complete it in a reasonable time. Applying deduction for the simple ones 
makes those rather boring. More time spend on writing down the numbers 
than on actually thinking and that irritating pen is in the way when 
write so you can not see part of the puzzle, annoying. I stopped doing 
the simple ones. ;)

> Isn't trial and error a form of deduction anyway?

I don't think it is. It is, however, a general and well known solving 
strategy.

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