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Collection July 2, 2012

 
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arkietech



Joined: 31 Jul 2008
Posts: 1733
Location: Northwest Arkansas USA

PostPosted: Mon Jul 02, 2012 6:43 am    Post subject: Collection July 2, 2012 Reply with quote

an old classic
Code:

 *-----------*
 |...|...|...|
 |..1|.2.|3..|
 |.3.|1.4|.5.|
 |---+---+---|
 |..6|...|2..|
 |.4.|...|.7.|
 |..8|...|9..|
 |---+---+---|
 |.1.|3.7|.4.|
 |..2|.9.|8..|
 |...|...|...|
 *-----------*
 

Play/Print online
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aran



Joined: 19 Apr 2010
Posts: 70

PostPosted: Mon Jul 02, 2012 10:46 am    Post subject: Reply with quote

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: 5178
Location: Rochester, NY, USA

PostPosted: Mon Jul 02, 2012 5:54 pm    Post subject: Reply with quote

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

PostPosted: Mon Jul 02, 2012 7:52 pm    Post subject: Reply with quote

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: 397

PostPosted: Tue Jul 03, 2012 1:17 pm    Post subject: Reply with quote

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

PostPosted: Tue Jul 03, 2012 7:53 pm    Post subject: Reply with quote

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 Smile
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ronk



Joined: 07 May 2006
Posts: 397

PostPosted: Tue Jul 03, 2012 9:59 pm    Post subject: Reply with quote

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. Smile

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 Smile

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

PostPosted: Wed Jul 04, 2012 12:17 pm    Post subject: Reply with quote

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: 3855

PostPosted: Wed Jul 04, 2012 3:31 pm    Post subject: Reply with quote

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 :

Maybe you should check the definition of inappropriate.
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Luke451



Joined: 20 Apr 2008
Posts: 310
Location: Southern Northern California

PostPosted: Wed Jul 04, 2012 6:19 pm    Post subject: Reply with quote

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. Smile

Source code files?? Very Happy Laughing Very Happy
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

PostPosted: Wed Jul 04, 2012 7:40 pm    Post subject: Reply with quote

Jeez, I'm not going to mess with any Luke comments on Sudoku history. Smile
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