Help with XY chains

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Help with XY chains

Postby chriswarren » Fri Oct 01, 2010 12:16 pm

Trying to solve the puzzle below via XY chains appears to give two eliminations for R1C4??

Starting from R1C6 -> R4C6-> R5C6->R6C4 -> suggests you can remove the 5 out of R1C4...

...and R1C6->R9C6->R7C4 -> suggests you can remove the 6 from R1C4!

Am I interpreting XY chains wrong? For each of the routes above, I believe I'm identifying strongly linked bi-value cells, and then removing a candidate from the cell (R1C4) that is seen by the pincer cells. Trouble is, these two chains above suggest removing both candidates from R1C4!!

Play this puzzle online at the Daily Sudoku site {link corrected}
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Re: Help with XY chains

Postby JasonLion » Fri Oct 01, 2010 12:25 pm

I can't get your link to work, even with some fixing up. I think that part of the actual URL is missing at the point where "..." appears.
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Re: Help with XY chains

Postby chriswarren » Fri Oct 01, 2010 6:53 pm

Hi Jason,

The link should be: {messed-up link removed -- see corrected in earlier post -- thanks, eleven !}

...I think I might have solved my problem though... I think I'm right in saying that the number you eliminate from the pincered cell must not be one that is used by the pincer end in connecting to the previous cell. i.e. in the above example, I cannot elimate the 6 from R1C4 because the 6 is used by the end of the pincer R7C4 to link with the previous cell in the chain.

Hope this right!
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Re: Help with XY chains

Postby eleven » Sat Oct 02, 2010 3:52 pm

You have to remove the spaces from the link
Code: Select all
+---------------+----------+---------------+
| 89   4    1   | 56 2  56 | 7    89  3    |
| 5678 567  578 | 9  3  4  | 1    268 2568 |
| 2    569  3   | 8  1  7  | 5    69  4    |
+---------------+----------+---------------+
| 5689 569  4   | 2  7  58 | 3    1   689  |
| 1789 2    789 | 3  6  18 | 4    5   89   |
| 1568 3    58  | 15 4  9  | 268  7   268  |
+---------------+----------+---------------+
| 3    159  59  | 16 89 2  | 568  4   7    |
| 1579 1579 6   | 4  89 3  | 258  28  1258 |
| 4    8    2   | 7  5  16 | 9    3   16   |
+---------------+----------+---------------+

Play this puzzle online at the Daily Sudoku site

chriswarren wrote:R1C6 -> R4C6-> R5C6->R6C4 -> suggests you can remove the 5 out of R1C4...

no, either R1C6=6 or R1C6=5 -> R4C6=8 -> R5C6=1 -> R6C4=5 gives no elimination

...and R1C6->R9C6->R7C4

this says either R1C6=5 or R1C6=6 -> R9C6=1 -> R7C4=6 no elimination either
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