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arkietech
Joined: 31 Jul 2008
Posts: 1834
Location: Northwest Arkansas USA
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 Posted: Mon Jul 02, 2012 6:43 am Post subject: Collection July 2, 2012 |
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an old classic
| Code: |
*-----------*
|...|...|...|
|..1|.2.|3..|
|.3.|1.4|.5.|
|---+---+---|
|..6|...|2..|
|.4.|...|.7.|
|..8|...|9..|
|---+---+---|
|.1.|3.7|.4.|
|..2|.9.|8..|
|...|...|...|
*-----------*
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Play/Print online |
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aran
Joined: 19 Apr 2010
Posts: 70
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| Posted: Mon Jul 02, 2012 10:46 am Post subject: |
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| Code: |
*-----------------------------------------------------------------------------*
| 5689 5689 579 | 56789 35678 35689 | 4 2 1 |
| 4 5689 1 | 56789 2 5689 | 3 689 6789 |
| 2 3 79 | 1 678 4 | 67 5 6789 |
|-------------------------+-------------------------+-------------------------|
| 1579 579 6 | 5789 134578 13589 | 2 138 3458 |
| 159 4 3 | 25689 1568 25689 | 156 7 568 |
| 157 2 8 | 567 134567 1356 | 9 136 3456 |
|-------------------------+-------------------------+-------------------------|
| 5689 1 59 | 3 568 7 | 56 4 2 |
| 3567 567 2 | 4 9 156 | 8 136 3567 |
| 35678 5678 4 | 2568 1568 12568 | 1567 1369 35679 |
*-----------------------------------------------------------------------------*
* |
DL-ALS 579r37c3 567r37c7
{975} {576} :=><9>r159c3 <6>r159c7 <7>r3c159 <5>r7c159 ste
A delightful symmetry which the DL-ALS structure reveals perhaps more elegantly than the associated loop
(7=9)r3c3-(9=5)r7c3-(5=6)r7c7-(6=7)r3c7 |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Mon Jul 02, 2012 5:54 pm Post subject: |
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I solved it with a bunch of moves, of which some were undoubtedly unnecessary.
Two Finned X-Wings
ER
XY-Loop
X-Wing
Last edited by Marty R. on Mon Jul 02, 2012 8:47 pm; edited 1 time in total |
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Luke451
Joined: 20 Apr 2008
Posts: 310
Location: Southern Northern California
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| Posted: Mon Jul 02, 2012 7:52 pm Post subject: |
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This puzzle does look very familiar. It's interesting that the only four bivalue cells on the grid form an xy-loop.
aran, thanks for pointing out the doubly-linked ALS approach. It's a stripped-down, natural example of the technique, no chain required.
I wonder if anyone remembers when this particular pattern had a name all its own? Although long subsumed, back in 2005 it was known by some as a Multivalue X-Wing.
If anyone is confused as to what exactly "doubly links" the two ALSs, these old graphics show it pretty clearly. |
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ronk
Joined: 07 May 2006
Posts: 398
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| Posted: Tue Jul 03, 2012 1:17 pm Post subject: |
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| Luke451 wrote: | It's interesting that the only four bivalue cells on the grid form an xy-loop.
...
I wonder if anyone remembers when this particular pattern had a name all its own? Although long subsumed, back in 2005 it was known by some as a Multivalue X-Wing.
If anyone is confused as to what exactly "doubly links" the two ALSs, these old graphics show it pretty clearly. |
The creation date shown on that page is 2008, and Andrew Stuart discontinued use of this technique in his solver.
The earlier term xy-ring coined AFAIK by Jeff in Forcing Chains: Terminology and Definition in 2006 is still in use today. BTW Jeff meant for the xy-ring term to be reserved for the shortest possible length of an xy-loop. |
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Luke451
Joined: 20 Apr 2008
Posts: 310
Location: Southern Northern California
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| Posted: Tue Jul 03, 2012 7:53 pm Post subject: |
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| ronk wrote: | | Luke451 wrote: | It's interesting that the only four bivalue cells on the grid form an xy-loop.
...
I wonder if anyone remembers when this particular pattern had a name all its own? Although long subsumed, back in 2005 it was known by some as a Multivalue X-Wing. |
The creation date shown on that page is 2008, and Andrew Stuart discontinued use of this technique in his solver.
The earlier term xy-ring coined AFAIK by Jeff in Forcing Chains: Terminology and Definition in 2006 is still in use today. BTW Jeff meant for the xy-ring term to be reserved for the shortest possible length of an xy-loop. |
I don't doubt the current site dates from 2008, but I have both the puzzles in that article pasted into my 2006 notebook. My origin note only says "Scanraid."
I'm down with xy-ring rather than loop for this one. I should have remembered, since I very recently saw it mentioned here. I see in that thread it was noted the xy-ring is also subsumed by doubly-linked ALS, which appears to be swallowing much of the known world  |
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ronk
Joined: 07 May 2006
Posts: 398
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| Posted: Tue Jul 03, 2012 9:59 pm Post subject: |
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| Luke451 wrote: | | I don't doubt the current site dates from 2008, but I have both the puzzles in that article pasted into my 2006 notebook. My origin note only says "Scanraid." |
I stand corrected, and am duly impressed. I've only a few source code files that are that old.
| Luke451 wrote: | | I'm down with xy-ring rather than loop for this one. I should have remembered, since I very recently saw it mentioned here. I see in that thread it was noted the xy-ring is also subsumed by doubly-linked ALS, which appears to be swallowing much of the known world |
Subsumption of a technique doesn't mean an existing term should be replaced though. Indeed, I think an ALS-anything term is inappropriate unless at least one cell has three or more candidates, i.e., is poly-valued. |
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aran
Joined: 19 Apr 2010
Posts: 70
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| Posted: Wed Jul 04, 2012 12:17 pm Post subject: |
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| ronk wrote: | | Indeed, I think an ALS-anything term is inappropriate unless at least one cell has three or more candidates, i.e., is poly-valued. |
This would appear to be semantics, at least I'm taking it to mean this :
if an ALMOST LOCKED SET were to lose its ALMOST status, then the remainder - to be semantically logical - should be a LOCKED SET, and not a resolved locked set, ie a set of assigneds.
More important is the logic of the concept, and grammar/semantics will just have to fall in behind. |
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daj95376
Joined: 23 Aug 2008
Posts: 3854
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| Posted: Wed Jul 04, 2012 3:31 pm Post subject: |
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| aran wrote: | | ronk wrote: | | Indeed, I think an ALS-anything term is inappropriate unless at least one cell has three or more candidates, i.e., is poly-valued. |
This would appear to be semantics, at least I'm taking it to mean this :
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Maybe you should check the definition of inappropriate. |
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Luke451
Joined: 20 Apr 2008
Posts: 310
Location: Southern Northern California
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| Posted: Wed Jul 04, 2012 6:19 pm Post subject: |
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| ronk wrote: | | Luke451 wrote: | | I don't doubt the current site dates from 2008, but I have both the puzzles in that article pasted into my 2006 notebook. My origin note only says "Scanraid." |
I stand corrected, and am duly impressed. I've only a few source code files that are that old. |
Source code files??  
Ron, you give me wa---aaay too much credit.
When I said I had those pasted in a notebook I meant I literally had them pasted in a notebook!
___ |
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DonM
Joined: 15 Sep 2009
Posts: 51
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| Posted: Wed Jul 04, 2012 7:40 pm Post subject: |
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| Jeez, I'm not going to mess with any Luke comments on Sudoku history. |
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