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Puzzle 11/08/17: ~ Advanced

 
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Wed Aug 17, 2011 2:02 pm    Post subject: Puzzle 11/08/17: ~ Advanced Reply with quote

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 . |
 +-----------------------+

Play this puzzle online at the Daily Sudoku site
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Marty R.



Joined: 12 Feb 2006
Posts: 5175
Location: Rochester, NY, USA

PostPosted: Fri Aug 19, 2011 4:55 am    Post subject: Reply with quote

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

PostPosted: Fri Aug 19, 2011 8:22 am    Post subject: Reply with quote

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

PostPosted: Fri Aug 19, 2011 9:46 am    Post subject: Reply with quote

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

PostPosted: Fri Aug 19, 2011 10:19 am    Post subject: Reply with quote

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

PostPosted: Fri Aug 19, 2011 11:24 am    Post subject: Reply with quote

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.. Wink

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 Very Happy
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