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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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 Posted: Sat Nov 29, 2008 8:13 pm Post subject: 11/28 competition |
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| Code: |
+-------+-------+-------+
| . . . | . . . | . 4 . |
| 2 . 4 | . . . | . . 7 |
| . . 1 | 4 8 7 | 6 . . |
+-------+-------+-------+
| 3 1 . | . . . | . . 2 |
| . . . | 3 . 8 | . . . |
| 7 . . | . . . | . 8 9 |
+-------+-------+-------+
| . 8 3 | 6 9 4 | . . . |
| 9 . . | . . . | 1 . . |
| . 5 . | . . . | . . . |
+-------+-------+-------+
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Play this puzzle online at the Daily Sudoku site | Code: | .---------------------.---------------------.---------------------.
| 8 367 67 | 259 2356 23569 | 59 4 1 |
| 2 36 4 | 159 1356 13569 | 8 59 7 |
| 5 9 1 | 4 8 7 | 6 2 3 |
:---------------------+---------------------+---------------------:
| 3 1 8 | 579 4567 569 | 457 56 2 |
| 46 2 9 | 3 57 8 | 57 1 46 |
| 7 46 5 | 12 1246 126 | 3 8 9 |
:---------------------+---------------------+---------------------:
| 1 8 3 | 6 9 4 | 2 7 5 |
| 9 467 267 | 2578 2357 235 | 1 36 468 |
| 46 5 267 | 1278 1237 123 | 49 369 468 |
'---------------------'---------------------'---------------------' |
| Quote: | nice skyscraper on 4
then a xy-chain in boxes 1 and 2 |
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daj95376
Joined: 23 Aug 2008
Posts: 3854
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| Posted: Sat Nov 29, 2008 11:55 pm Post subject: |
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| Quote: | Instead of XY-Chain, there's probably a BUG+3 logic that I don't understand.
What I do understand is:
(27) UR [r89c35] => [r8c5]<>7, [r9c5]<>2
BUG+1
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Asellus
Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA
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| Posted: Sun Nov 30, 2008 1:19 am Post subject: |
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I can't follow Danny's UR logic.
Norm's Skyscraper elimination can also be seen as a Kite. Then, instead of an XY Chain, there is an interesting UR based "XY Wing":
| Code: | +----------+-----------------+-------+
| 8 7 6 | 29 @23 239 | 5 4 1 |
| 2 3 4 | 15 16 156 | 8 9 7 |
| 5 9 1 | 4 8 7 | 6 2 3 |
+----------+-----------------+-------+
| 3 1 8 | 79 67 69 | 4 5 2 |
| 4 2 9 | 3 5 8 | 7 1 6 |
| 7 6 5 | 12 4 12 | 3 8 9 |
+----------+-----------------+-------+
| 1 8 3 | 6 9 4 | 2 7 5 |
| 9 4 [27] | 257 $3[27] 235 | 1 6 8 |
| 6 5 [27] | 8 $1[27] @12 | 9 3 4 |
+----------+-----------------+-------+ |
The 27UR in r89c35 creates a {13} pseudo-cell ($) in r89c5 from which we get a 123 XY Wing with <2> pincers at @. <2>s are eliminated from r1c6 and r89c5. |
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daj95376
Joined: 23 Aug 2008
Posts: 3854
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| Posted: Sun Nov 30, 2008 3:49 am Post subject: |
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| Asellus wrote: | | I can't follow Danny's UR logic. |
| Code: | +-----------------------------------------------------+
| 8 7 6 | 29 23 39 | 5 4 1 |
| 2 3 4 | 15 16 56 | 8 9 7 |
| 5 9 1 | 4 8 7 | 6 2 3 |
|-----------------+-----------------+-----------------|
| 3 1 8 | 79 67 69 | 4 5 2 |
| 4 2 9 | 3 5 8 | 7 1 6 |
| 7 6 5 | 12 4 12 | 3 8 9 |
|-----------------+-----------------+-----------------|
| 1 8 3 | 6 9 4 | 2 7 5 |
| 9 4 27 | 257 3+27 35 | 1 6 8 |
| 6 5 27 | 8 1+27 12 | 9 3 4 |
+-----------------------------------------------------+
# 21 eliminations remain
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Old-style UR logic. At least one of [r8c5]=3, [r9c5]=1 must be true for (27) UR in [r89c35].
| Code: | [r8 c5]=3 => [r8c5]<>7
[r924c5]=167 => [r8c5]<>7 q.e.d.
[r9 c5]=1 => [r9c5]<>2
[r81 c5]=32 => [r9c5]<>2 q.e.d.
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I've used this approach in the past, but never knew if it had a number.
[Edit: corrected typo noticed by Asellus. Thanks!]
Last edited by daj95376 on Sun Nov 30, 2008 4:01 pm; edited 1 time in total |
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Asellus
Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA
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| Posted: Sun Nov 30, 2008 8:46 am Post subject: |
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First of all, I misunderstood and thought you were applying the UR before using the Skyscraper/Kite on 4. My mistake.
After the Skyscraper/Kite, I would see it as a Type "6A", according to which r8c5<>2 since this forces the DP. This is based on the conjugate <7>s in c3 and r9 and the 27 bivalues at r89c3. Your reasoning that r8c5<>7 and r9c5<>2 (not r9c1, I assume) based on resulting locked sets is interesting. Combining the two approaches determines that r8c5=3.
I am embarrassed that I didn't notice the 12 locked pair in c6  . The pseudocell XY Wing results immediately in r8c5=3 as well. So, it seems to be another way to see the same thing. |
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