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Trouble understanding sashimi fish

 
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sctprog



Joined: 29 Jun 2016
Posts: 2
PostPosted: Wed Jun 29, 2016 10:27 pm    Post subject: Trouble understanding sashimi fish Reply with quote
I'm having a bit of trouble understanding sashimi fish. Here's an example board:

Code:

+------------+-----------+-----------+
| 7   369 28 | 1   28 4  | 5 369 69  |
| 39  389 4  | 5   28 6  | 7 139 129 |
| 26  1   5  | 37  9  37 | 4 26  8   |
+------------+-----------+-----------+
| 8   2   36 | 347 5  37 | 1 69  469 |
| 49  49  1  | 2   6  8  | 3 5   7   |
| 5   7   36 | 34  1  9  | 2 8   46  |
+------------+-----------+-----------+
| 146 46  7  | 8   3  2  | 9 14  5   |
| 13  38  28 | 9   4  5  | 6 7   12  |
| 24  5   9  | 6   7  1  | 8 24  3   |
+------------+-----------+-----------+


By my understanding, there is a sashimi x-wing for candidate 2 on row 2, c5/c9 and row 8 c3/c9 allowing elimination from r1c3.

This isn't actually a valid elimination but I don't know why. Would someone be willing to explain it please?

Thanks!
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Thu Jun 30, 2016 9:59 pm    Post subject: Re: Trouble understanding sashimi fish Reply with quote
sctprog wrote:
I'm having a bit of trouble understanding sashimi fish. Here's an example board:

Code:

+------------+-----------+-----------+
| 7   369 28 | 1   28 4  | 5 369 69  |
| 39  389 4  | 5   28 6  | 7 139 129 |
| 26  1   5  | 37  9  37 | 4 26  8   |
+------------+-----------+-----------+
| 8   2   36 | 347 5  37 | 1 69  469 |
| 49  49  1  | 2   6  8  | 3 5   7   |
| 5   7   36 | 34  1  9  | 2 8   46  |
+------------+-----------+-----------+
| 146 46  7  | 8   3  2  | 9 14  5   |
| 13  38  28 | 9   4  5  | 6 7   12  |
| 24  5   9  | 6   7  1  | 8 24  3   |
+------------+-----------+-----------+


By my understanding, there is a sashimi x-wing for candidate 2 on row 2, c5/c9 and row 8 c3/c9 allowing elimination from r1c3.

This isn't actually a valid elimination but I don't know why. Would someone be willing to explain it please?

Thanks!


Since the 2s in r2c9 and r8c9 cannot both be true,either r2c5 or r8c3 MUST be =2 and any 2 that sees both those cells can be eliminated. However, structurally, r2 and 9 form a Skyscraper, not a Sashimi. The latter would normally have three occurrences in one of the rows.

I hope there's something in this thread that might be helpful.

http://www.dailysudoku.co.uk/sudoku/forums/viewtopic.php?t=5390
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sctprog



Joined: 29 Jun 2016
Posts: 2
PostPosted: Fri Jul 01, 2016 6:29 pm    Post subject: Reply with quote
Ah I'm using the wrong term. Sudoku 10k+ calls it a Sashimi X-Wing, not a Skyscraper.. but we're talking about the same pattern.

The link you gave explains my misunderstanding though.

Thank you for your reply!
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