19 Apr '08 16:061 edit

I am just curious if anyone knows whether or not bifurcation or the "brute force" method is sometimes absolutely necessary to solve one of the tougher Sudoku

For those of you who don't know bifurcation refers to when you try out each possibility for a locatio for which it could be a limited number of options (usually only 2), and then eliminate the one which leads to a contradiction. It is a last-resort method of sorts.

Several of the harder sudoku seem to require use of this technique, because I have found myself unable to discern or eliminate any of the remaining options using any other method.

This one for instance..

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I managed to get it this far without brute force/guessing.

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Any other super-advanced techniques or logic which could proceed forward from this point?

For those of you who don't know bifurcation refers to when you try out each possibility for a locatio for which it could be a limited number of options (usually only 2), and then eliminate the one which leads to a contradiction. It is a last-resort method of sorts.

Several of the harder sudoku seem to require use of this technique, because I have found myself unable to discern or eliminate any of the remaining options using any other method.

This one for instance..

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**6**~~~~~~**84**~**3**~**2**~~~**32**~~~**5**~**74**~

**6**~~**9**~**8**~~~~~

**624**~~~~~

**2**~**3**~~**6**~**21**~**9**~~~**87**~~~

**4**~**3**~**25**~~~~~~

**1**~~I managed to get it this far without brute force/guessing.

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**6**~**49238****84**~**3**~**25**~~**32**~~~**5**~**74****463**~**9**~**8**~**2**~~~

**6247**~**3**~~

**2**~**3**~**46**~**214956387**~~~

**413**~**25**~

**352**~~**14**~Any other super-advanced techniques or logic which could proceed forward from this point?