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daj95376
Joined: 23 Aug 2008
Posts: 3854
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 Posted: Wed Aug 17, 2011 2:02 pm Post subject: Puzzle 11/08/17: ~ Advanced |
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| Code: | +-----------------------+
| 3 . 6 | . . . | 4 1 . |
| . . . | . . . | . . . |
| 7 . 4 | . . 3 | . . 2 |
|-------+-------+-------|
| . . . | 6 . . | 9 . 7 |
| . . . | . 5 . | 2 3 6 |
| . . 7 | . . 9 | . 5 4 |
|-------+-------+-------|
| 5 . . | 4 7 . | . . 9 |
| 4 . . | . 9 6 | . . 1 |
| . . 9 | 2 3 5 | 7 4 . |
+-----------------------+
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Play this puzzle online at the Daily Sudoku site |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Fri Aug 19, 2011 4:55 am Post subject: |
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XYZ-Wing (278); r2c6<>8
XY-Wing (182), flightless with transport; r2c3<>2
Multi-coloring; r4c1<>1 |
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SudoQ
Joined: 02 Aug 2011
Posts: 127
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| Posted: Fri Aug 19, 2011 8:22 am Post subject: |
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I tested this puzzle in the HoDoKu solver, that started with a Skyscraper: | Code: | | 1 in r2c3, r3c4 (connected by r5c34) => r2c5, r3c2 <> 1. |
The automatic solver then uses two more steps.
However, it is easy to show that r4c6<>2, which solves the puzzle: | Code: | | r4c6=2 => r4c2=1 => r2c3=1&2. |
I don't know if this method has a name, or if it is considered to be trial and error?
/SudoQ |
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peterj
Joined: 26 Mar 2010
Posts: 974
Location: London, UK
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| Posted: Fri Aug 19, 2011 9:46 am Post subject: |
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| SudoQ wrote: | I don't know if this method has a name, or if it is considered to be trial and error?
/SudoQ |
As you have described it, I would call it a "contradiction forcing chain". In that you assume a truth and then show it leads to a contradiction, hence your assumption is false.
This move is certainly "assumptive" unlike patterns and AIC chains which make no assumptions about the truth of their propositions. Many would think it is one step closer to T&E...
Many of these chains can be written as AIC - but not always. |
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SudoQ
Joined: 02 Aug 2011
Posts: 127
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| Posted: Fri Aug 19, 2011 10:19 am Post subject: |
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OK, thank you!
| peterj wrote: | | Many of these chains can be written as AIC - but not always. |
May I ask if this particular chain could be expressed as an AIC?
/SudoQ |
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peterj
Joined: 26 Mar 2010
Posts: 974
Location: London, UK
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| Posted: Fri Aug 19, 2011 11:24 am Post subject: |
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| SudoQ wrote: | | May I ask if this particular chain could be expressed as an AIC? |
Without knowing exactly what was in your head it's hard to know.. 
But assuming it was concerning the strong link on 1 and strong link on 2 in row 2 which converge on r2c3 then...
| Code: | | (2=1)r4c1 - r2c1=(1-2)r2c3=r2c6 ; r4c6<>2 |
This AIC states that either r4c1=2 or r2c6=2 - it does not assume either is true but it proves that one or both must be true. Hence any cell that sees both <>2.
This is in fact an m-wing. Nice  |
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