Sped wrote:
I don't see that as a closed chain. I see it as a regular XY chain starting on r7c6 and meandering to r1c7. It has loose 9s on each end so it allows the elimination of 9s in cells that see both r7c6 and r1c7.. in this case r1c6 and r7c7.
I'd write it like this:
9-(r7c6)-6-(r8c4)-9-(r8c9)-3-(r7c8)-4-(r3c8)-3-(r1c7)-9
I see. It is actually a matter of perspective. The difference in our perspectives is that yours is useful, practical and easy, whereas mine is inflexible and limited. Other than that, they are identical. I had always looked for xy-chains by finding the bivalue cells and then searching for loops that contradicted the pilot cell. If I didn't get a contradiction, then I knew that I would have the opportunity to make some deductions outside of the loop. What your post tells me is that it is more effective to start with a bivalue cell with candidates (XY) and follow a chain until you reach a cell with candidates (ZX). Now make eliminations of X in any cell seeing the pilot cell and the terminal cell. But you don't have to stop there. If you haven't enough eliminations, try extending the chain. If you keep your eyes open, you might find a subchain of use.
This seems to have the advantage of being shorter, more likely to spot deductions in polyvalued cells and, as my example shows, makes it easier to see additional eliminations.
Thanks for the insight!
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