>"Rock Brentwood" <email@example.com> wrote in message >news:firstname.lastname@example.org... >[snip..] > > >>The REAL issue is that to solve a Sudoku grid, there are actually TWO >>parts: (a) find a solution (i.e. prove that one exists), but also (b) >>prove that it is the ONLY solution. >> >> > >I've never come across a sudoku variant where part of the objective was to >prove the solution is unique. In contrast, many sudoku puzzles actually >state up front that the solutions are unique as one of the puzzle >constraints, and the ones that don't do this *are* in fact always unique, >i.e. they have just made the constraint a "secret rule" of the puzzle >(grrrr!). >
It's no secret. But if there is not a unique solution, the solver by necessity gets to a point where the "next step" is no longer logically implied by the structure of the puzzle. That is, you have several equally valid guesses, all of which lead to a solution. That defeats the whole purpose of the puzzle.
-- Stephen J. Herschkorn email@example.com Math Tutor on the Internet and in Central New Jersey and Manhattan