Sudoku solver

[Marko Rauhamaa]

Ian Kelly <ian.g.kelly at gmail.com>:

> I don't think that I have used trial and error, in my head or
> otherwise, in any sudoku I have ever solved.

Of course you have. "This here can't be a 2 because if it were a 2, that
there would have to be a 5, which is impossible. Thus, the only
remaining alternative is 3, so I mark that down."

That's trial and error, aka, reductio ad absurdum.

(Additionally, sudoku solvers are known to pencil all kinds of markings
on the sudoku sheets to help the deduction work.)


Marko