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LA Times/Freep - July 25, 2008

 
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Sat Jul 26, 2008 2:58 am    Post subject: LA Times/Freep - July 25, 2008 Reply with quote

Code:
+-------+-------+-------+
| . 8 . | . 9 . | . . . |
| . 3 . | . . . | . . 4 |
| . . . | . 8 6 | 2 . . |
+-------+-------+-------+
| . . . | . 1 . | . 7 . |
| 3 . . | 4 . 9 | . . 1 |
| . 4 . | . . . | . . . |
+-------+-------+-------+
| . . 6 | 1 7 . | . . . |
| 8 . . | . . . | . 5 2 |
| . . . | . . . | . 8 . |
+-------+-------+-------+
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Sat Jul 26, 2008 11:57 am    Post subject: Reply with quote

Two overlapping type 6 (or hidden) UR's leave 1 in r1c3.

And then - lets try to find a finned xy-wing.
Code:
 *--------------------------------------------------*
 |#27   8    1    | 27   9    4    | 6    3    5    |
 | 6    3    27   | 257 *25   1    | 8    9    4    |
 | 49   5    49   | 3    8    6    | 2    1    7    |
 |----------------+----------------+----------------|
 |-29   6    259  | 8    1   *25   | 4    7    3    |
 | 3    7    8    | 4    26   9    | 5    26   1    |
 | 1    4    25   | 256  3    7    | 9    26   8    |
 |----------------+----------------+----------------|
 | 5    2    6    | 1    7    8    | 3    4    9    |
 | 8    19   47   | 69   46   3    | 17   5    2    |
 |#47   19   3    | 259 #245  25   | 17   8    6    |
 *--------------------------------------------------*

Either the fin r9c5=5 or (xy-wing 247) one of r1c1 and r9c5 is 2.
r9c5=5 => r2c5=2 => r1c1=2.
r9c5=2 => r4c6=2.
So we can eliminate 2 from r4c1.
[Edit: corrected typo]


Last edited by ravel on Sat Jul 26, 2008 8:05 pm; edited 1 time in total
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sat Jul 26, 2008 1:01 pm    Post subject: Reply with quote

I see the Type 6 UR using 27 - but I have 127 in R1C3 - so I'm left with a 12 not a 1. I must have missed something in basics though I can't see what.
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Marty R.



Joined: 12 Feb 2006
Posts: 5164
Location: Rochester, NY, USA

PostPosted: Sat Jul 26, 2008 3:33 pm    Post subject: Reply with quote

cgordon wrote:
I see the Type 6 UR using 27 - but I have 127 in R1C3 - so I'm left with a 12 not a 1. I must have missed something in basics though I can't see what.

Craig,

Because 7 is a strong link in row 2, 7 can be eliminated from r1c3 to break up a deadly pattern. That exposes a true Type 6 UR on 12, forcing r1c3 and r1c6 to both be 1.

After that I couldn't find anything and used Medusa traps to finish it off.
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Sat Jul 26, 2008 9:43 pm    Post subject: Reply with quote

I find that XY Chains (as well as Type 1, and sometimes Type 4, URs) are frequently useful in these LAT/Freep puzzles. In this case, the 4-cell chain
(2=7)r2c3 - (7=4)r8c3 - (4=6)r8c5 - (6=2)r5c5
removes <2> from r2c5 and converts that UR to a simple Type 1.

Meanwhile, as the recent posted examples have shown, these "Finned XY Wing" things are surely versatile in their possible inner workings! I like them because they allow one to find what are essentially unidirectional AICs that would otherwise be very obscure to discover.
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