A Fishing Question

Advanced methods and approaches for solving Sudoku puzzles

A Fishing Question

Postby keith » Sun Feb 11, 2007 10:21 pm

I have been contemplating X-wings when one of the strong links is not in a row or column, but in a box. Along the way, I found this interesting specimen. It is the Daily Sudoku of Jan 15:
Code: Select all
Puzzle: DS011507
+-------+-------+-------+
| . 7 6 | . 9 . | . 8 . |
| . . 2 | . . 3 | . . 9 |
| . 3 . | 6 . . | . . . |
+-------+-------+-------+
| 1 . . | 5 . . | . . . |
| . 6 9 | . 2 . | 4 3 . |
| . . . | . . 6 | . . 8 |
+-------+-------+-------+
| . . . | . . 1 | . 5 . |
| 6 . . | 2 . . | 8 . . |
| . 2 . | . 5 . | 1 7 . |
+-------+-------+-------+

Basic moves will get you to this sticking point:
Code: Select all
DS011507
+----------------+----------------+----------------+
| 5    7    6    | 4    9    2    | 3    8    1    |
| 48   148  2    | 78   178# 3    | 5    6    9    |
| 9    3    18c  | 6    18C  5    | 7    4    2    |
+----------------+----------------+----------------+
| 1    48   348# | 5    348b 9    | 6    2    7    |
| 78   6    9    | 1    2    78B  | 4    3    5    |
| 2    45   3457 | 37   347  6    | 9    1    8    |
+----------------+----------------+----------------+
| 478  9    478# | 38   6    1    | 2    5    34   |
| 6    15   15   | 2    37   47   | 8    9    34   |
| 3    2    48a  | 9    5    48A  | 1    7    6    |
+----------------+----------------+----------------+

I believe the intended way forward is an XY-wing, but I have marked an interesting fishy thingy.

It is actually a swordfish on <8>, the strong links (conjugate pairs) are aA, bB, and cC. aA is in R9, bB is in B5, and cC is in R3. The usual swordfish logic applies, and the eliminations are in the cells marked #.

Can anyone tell me the name of this creature, and provide more insights or point me to discussions?

Thank you,

Keith
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re: A Fishing Question

Postby Pat » Mon Feb 12, 2007 9:53 am

keith wrote:
Code: Select all
+----------------+----------------+----------------+
| 5    7    6    | 4    9    2    | 3    8    1    |
| 48   148  2    | 78   178# 3    | 5    6    9    |
| 9    3    18c  | 6    18C  5    | 7    4    2    |
+----------------+----------------+----------------+
| 1    48   348# | 5    348b 9    | 6    2    7    |
| 78   6    9    | 1    2    78B  | 4    3    5    |
| 2    45   3457 | 37   347  6    | 9    1    8    |
+----------------+----------------+----------------+
| 478  9    478# | 38   6    1    | 2    5    34   |
| 6    15   15   | 2    37   47   | 8    9    34   |
| 3    2    48a  | 9    5    48A  | 1    7    6    |
+----------------+----------------+----------------+



It is actually a swordfish on <8>, the strong links (conjugate pairs) are aA, bB, and cC. aA is in R9, bB is in B5, and cC is in R3. The usual swordfish logic applies, and the eliminations are in the cells marked #.

Can anyone tell me the name of this creature, and provide more insights or point me to discussions?



yes, it is a Franken Swordfish rrb\ccc:
r39b5\c356
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Postby Carcul » Mon Feb 12, 2007 11:11 am

Keith wrote:It is actually a swordfish on <8>, ...


I see it as a continuous nice loop:

[r3c3]=8=[r3c5]-8-[r4c5]=8=[r5c6]-8-[r9c6]=8=[r9c3]-8-[r3c3], => r2c5/r4c3/r7c3<>8.

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