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| rkral
| | Joined: 21 Oct 2005 | | Posts: 233 | | : | |
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 Posted: Tue Feb 28, 2006 11:28 am Post subject: Re: Coloring |
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| orlp wrote: | | It is entirely unnecessary to prove also that if r9c7 is not 4 then r3c9 is 4 since that follows by logical equivalence ... |
OK, let me paraphrase your argument. Either r3c9=4 or r3c9<>4.
If r3c9=4 then r7c9<>4
If r3c9<>4 then r3c6=4, r9c6<>4, r9c7=4 and r7c9<>4
For both r3c9=4 and r3c9<>4, r7c9<>4
Therefore, r7c9<>4
The logic is impeccable, so I stand corrected. I don't think I would've considered "coloring" as a suitable technique for that, so thanks for that POV.
Ron |
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| orlp
| | Joined: 25 Feb 2006 | | Posts: 4 | | : | |
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| Posted: Tue Feb 28, 2006 10:30 pm Post subject: |
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OK Now we're agreed on the idea.
The question is: is this a useful technique? While I'm certain of its validity, I'm not so sure about this. It does solve some multicolor situations, but the pattern is much less visible than the true "symmetric" colouring situations, where the pairs stand out, once you've got used to seeing them.
On the other hand, for me it seems a lot easier than "forcing chains", which is too close to trial and error for my taste.
Oliver |
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