Darren New <dne### [at] sanrrcom> wrote:
> >   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.

> I think you might need some backtracking in the hardest of problems.

  Thinking about it, in fact I think the only requirement for a sudoku
puzzle to be rational is that it must have only one possible solution.
As far as I understand, all sudoku puzzles are like that.

  The difficulty of the puzzle is determined by how deep your deductions
must be if you want to solve it with certainty (ie. without trial and error).

-- 
                                                          - Warp

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