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27 jan VH

 
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roaa



Joined: 18 Apr 2009
Posts: 78
Location: Sweden

PostPosted: Fri Jan 27, 2012 7:39 am    Post subject: 27 jan VH Reply with quote

An xyz-wing(128) solved this puzzle for me.
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TerenceF



Joined: 21 Dec 2007
Posts: 19
Location: Takapuna, NZ

PostPosted: Sun Jan 29, 2012 12:52 am    Post subject: Reply with quote

Roaa's XYZ wing is clearly visible at r4c2 in this grid, but I didn't spot it Sad

Code:

+------------+------------+---------+
| 19 149 139 | 237 27  8  | 5  6 47 |
| 6  48  38  | 37  5   1  | 2  9 47 |
| 5  7   2   | 9   6   4  | 8  1 3  |
+------------+------------+---------+
| 28 128 6   | 12  4   9  | 3  7 5  |
| 4  3   159 | 17  8   57 | 19 2 6  |
| 7  129 159 | 6   3   25 | 19 4 8  |
+------------+------------+---------+
| 28 6   89  | 4   29  3  | 7  5 1  |
| 3  12  4   | 5   127 27 | 6  8 9  |
| 19 5   7   | 8   19  6  | 4  3 2  |
+------------+------------+---------+


Instead, I managed to prove that r1c2<>9 by following the chain IF r1c1=9 then r1c2<>9 AND if r1c1=1 then r9c1=9 so r7c3=8 so r2c3=3 so r1c3=9 so r1c2<>9. (I don't know the right name for this kind of chain)

Eliminating 9 from r1c2 leaves r2c6 as the only option for 9 in column 2 ... which is the same outcome as you get if you spot roaa's elegant XYZ wing. Wink

So I used a horribly complicated route to get to the same result.

I guess what I need to learn is a technique for searching out XYZ wings, because my brain starts looking for complicated chains and I so often miss the simple wings.

Any ideas anyone?
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Marty R.



Joined: 12 Feb 2006
Posts: 5166
Location: Rochester, NY, USA

PostPosted: Sun Jan 29, 2012 1:01 am    Post subject: Reply with quote

Quote:
I guess what I need to learn is a technique for searching out XYZ wings, because my brain starts looking for complicated chains and I so often miss the simple wings.

Any ideas anyone?

Maybe someone has some efficient ways, but for me it's just grunt work. One by one, I examine each box to see if it contains a trivalue cell. If yes, then see if the box has a bivalue cell with two of the numbers that are in the trivalue. If yes, see if there's another bivalue cell that fits the pattern in the same line or column as the trivalue cell.

Then just keep moving from box to box. It really doesn't take as long as it sounds like.
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