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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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 Posted: Tue May 10, 2011 3:01 pm Post subject: Interesting move |
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This one came down to an interesting last move.
| Code: | Puzzle: M4774112sh(18)
+-------+-------+-------+
| . . . | . 7 . | . . . |
| . . . | . 8 . | . . 4 |
| . 7 . | . . . | 6 . 9 |
+-------+-------+-------+
| 2 . . | . 1 . | 8 4 . |
| . . 3 | . . . | . . . |
| . 4 . | 9 . . | . 7 . |
+-------+-------+-------+
| 4 . . | . . . | 2 . 6 |
| . 6 . | 1 . 3 | . . . |
| . . . | . 5 2 | . . . |
+-------+-------+-------+ |
Keith |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Tue May 10, 2011 4:42 pm Post subject: |
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XYZ-Wing (138); r9c1<>3
Hidden UR (13); r9c2<>3
Type 3 UR (89) needs a 1 or 3. The 1 proves a 3; pincers set r2c8<>3 |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Tue May 10, 2011 9:31 pm Post subject: |
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After basics: | Code: | +----------------+----------------+----------------+
| 3568 238 489 | 245 7 69 | 1 2358 38 |
| 1356 123 19 | 25 8 69 | 7 235 4 |
| 58 7 48 | 245 3 1 | 6 258 9 |
+----------------+----------------+----------------+
| 2 9 6 | 3 1 7 | 8 4 5 |
| 7 5 3 | 8 2 4 | 9 6 1 |
| 18 4 18 | 9 6 5 | 3 7 2 |
+----------------+----------------+----------------+
| 4 13 5 | 7 9 8 | 2 13 6 |
| 89 6 2 | 1 4 3 | 5 89 7 |
| 1389 138 7 | 6 5 2 | 4 1389 38 |
+----------------+----------------+----------------+ |
Marty, I originally had more moves that you did, but my final move turns out to be present in the grid above, and is a one-stepper.
Take a look at the 13 UR in R79C28. To avoid the DP, R8C1 must be <9>.
I'll leave it to ronk, Danny, and peterj to classify this one, if they so wish.
Keith |
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daj95376
Joined: 23 Aug 2008
Posts: 3854
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| Posted: Tue May 10, 2011 9:55 pm Post subject: |
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I'm not exactly sure of the logic Keith employed for his elimination:
| Code: | (8)r9c2 - (8=9)r8c1
(8)r9c8 - r3c8 = r3c13 - r1c2 = r9c2 - (8=9)r8c1
(9)r9c8 - (9=8)r8c8 - (8=9)r8c1
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You just need to ignore that r9c8=8 and r9c2=8 occur in the second stream. Fortunately, chains are like that!
My solver found numerous eliminations associated with the <13> UR. However, I played around with the UR and manually derived a ...
1-SIS ALS single-stepper:
| Code: | (8)r9c2 =UR= (89)r98c8 => r9c9<>8
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Tue May 10, 2011 11:24 pm Post subject: |
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| Quote: | | Take a look at the 13 UR in R79C28. To avoid the DP, R8C1 must be <9>. |
I did take a look and don't have a clue why. Standard internal analysis doesn't do it for me. |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Tue May 10, 2011 11:41 pm Post subject: |
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| daj95376 wrote: | | I'm not exactly sure of the logic Keith employed |
I saw there is an 89 pseudocell in the UR, and tried to make some sense of it.
R8C1 <8> forces the deadly pattern.
Keith |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Wed May 11, 2011 12:53 am Post subject: |
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| daj95376 wrote: | | I'm not exactly sure of the logic Keith employed |
That would put you 100% on board with my wife and the rest of my family!
(Of course, they are not talking Sudoku.)
Keith |
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