Y-wing-meets-finned-swordfish

Advanced methods and approaches for solving Sudoku puzzles

Y-wing-meets-finned-swordfish

Postby 999_Springs » Sun Feb 03, 2008 10:05 pm

Code: Select all
5   34   17 |1367 8   36 |19 1469 2
147 8    6  |9    14  2  |3  147  5
49  2349 127|1367 146 5  |8  146  17
------------+------------+----------
14  1246 127|13   9   368|5  18   17
3   17   5  |14   2   48 |6  178  9
8   16   9  |5    16  7  |2  3    4
------------+------------+-----------
6   59   4  |2    3   1  |7  59   8
179 179  8  |46   5   46 |19 2    3
2   15   3  |8    7   9  |4  15   6

I was working on this puzzle and I got here after some swordfishes and turbot etc and I found something that looks like a Y-wing crossed with a finned swordfish.

Finned swordfish in 1: r269c258, fin r2c1
Bivalue cells: r1c3, r5c2
r4c3<>7

(If r4c3=7 then this forces three 1s to be in columns 5 and 8 which is impossible.)

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Re: Y-wing-meets-finned-swordfish

Postby Sudtyro » Mon Feb 04, 2008 3:05 am

[Edit: Withdrawn.]
Last edited by Sudtyro on Mon Feb 04, 2008 8:32 am, edited 1 time in total.
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Postby Mike Barker » Mon Feb 04, 2008 4:34 am

The elimination is what I've called a Kraken Fish. "Kraken" comes from the extra "tentacles" on the fish creating the elimination. The bivalue cells link the candidate elimination cell to the fin and one of the covering sets (c2). Still looking for a good way to show this type of elimination. I've been gravitating towards the chain I've shown because it shows both the restricted set (the fish) and the strong inference set and works for kraken fish, URs, BUG-Lites, AHS, etc.

Code: Select all
Kraken Fish -7- r1c3 -1- Swordfish:r269c258(r2c1 =1= r69c2) -1- r5c2 -7- => r4c3<>7
5    34   17a |1367 8   36 |19 1469 2
147@ 8    6   |9    14* 2  |3  147* 5
49   2349 127 |1367 146 5  |8  146  17
--------------+------------+----------
14   1246 12-7|13   9   368|5  18   17
3    17b  5   |14   2   48 |6  178  9
8    16*  9   |5    16* 7  |2  3    4
--------------+------------+-----------
6    59   4   |2    3   1  |7  59   8
179  179  8   |46   5   46 |19 2    3
2    15*  3   |8    7   9  |4  15*  6


Edit: I've also often shown the elimination on multiple lines, this works well when dealing with multi-inference nice loops.
Code: Select all
Kraken Fish (r269c258=1):
r2c1 -1- r1c3 -7-
||                        => r4c3<>7
r69c2 -1- r5c2 -7-
Last edited by Mike Barker on Mon Feb 04, 2008 10:06 am, edited 1 time in total.
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Postby daj95376 » Mon Feb 04, 2008 6:48 am

Mike Barker, I agree that it's a Kraken Swordfish, but I prefer the following interpretation.

Code: Select all
Kraken Swordfish r269\c258 with exterior cell [r2c1]

Swordfish r269\c258               => [r5c2]<>1
[r2c1]-1-[r1c3]-7-[r4c3]=7=[r5c2] => [r5c2]<>1
+--------------------------------------------------------------------+
|  5      34     17    |  1367   8      36    |  19     1469   2     |
| @147    8      6     |  9     *14     2     |  3     *147    5     |
|  49     2349   127   |  1367   146    5     |  8      146    17    |
|----------------------+----------------------+----------------------|
|  14     1246   127   |  13     9      368   |  5      18     17    |
|  3      7-1    5     |  14     2      48    |  6      178    9     |
|  8     *16     9     |  5     *16     7     |  2      3      4     |
|----------------------+----------------------+----------------------|
|  6      59     4     |  2      3      1     |  7      59     8     |
|  179    179    8     |  46     5      46    |  19     2      3     |
|  2     *15     3     |  8      7      9     |  4     *15     6     |
+--------------------------------------------------------------------+

Everything, except intermediate cells in the chain, is based on candidate 1.
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Postby Mike Barker » Mon Feb 04, 2008 1:49 pm

That is an equally valid interpretation. I have found that I understand the elimination better if the Strong Inference Set (SIS) is clearly defined. After all that was the whole point of the Sudoku Unification Model. Once the SIS is defined, whether it be derived from fish, cell, unit, UR, BUG-Lite, ALS, AHS, AALS, almost nice loop, etc., its pretty clear how to link it into an implication chain. Further using the SIS for multi-inference eliminations is also straight forward - "simply" link each element of the SIS, either individually or as groups, so that an elimination can take place. Its a POV I've found very useful. It worked very well in helping to find solutions to Andrew's Unsolvables.
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Postby ronk » Mon Feb 04, 2008 4:54 pm

Since it's much more fish-like for a kraken fish elimination to be a direct elmination when all the fin cells are false, IMO daj95376's POV is clearly the better POV.
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