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arkietech
Joined: 31 Jul 2008
Posts: 1834
Location: Northwest Arkansas USA
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 Posted: Sun Aug 19, 2012 6:48 am Post subject: Daily Telegraph Diabolical Fri, 17-Aug-2012 |
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| Code: |
*-----------*
|...|..9|...|
|43.|8..|.29|
|..9|.5.|1..|
|---+---+---|
|..6|57.|...|
|.54|...|2..|
|...|..1|3..|
|---+---+---|
|..2|.3.|5..|
|96.|...|.81|
|...|4..|...|
*-----------*
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Play/Print this puzzle online |
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Clement
Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania
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| Posted: Sun Aug 19, 2012 10:16 am Post subject: Daily Telegraph Diabolical Fri, 17-Aug-2012 |
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After the Basics | Code: |
+-----------+------------+------------+
| 26 27 1 | 236 46 9 | 8 457 3-457 |
| 4 3 5 | 8 1 7 | 6 2 9 |
| -268 -278 9 | 236 5 24 | 1 -47 347 |
+-----------+------------+------------+
| 3 28 6 | 5 7 24 | 9 1 48 |
| 1 5 4 | 9 68 3 | 2 67 78 |
| 28 9 7 | 26 46-8 1 | 3 456 458 |
+-----------+------------+------------+
| 7 4 2 | 1 3 8 | 5 9 6 |
| 9 6 3 | 7 2 5 | 4 8 1 |
| 5 1 8 | 4 9 6 | 7 3 2 |
+-----------+------------+------------+
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Four Short Adv Moves.
XY-Wing 26 46 24 pivoted in r1c5; r3c12<>2
XY-Wing 28 26 68 pivoted in r6c4; r6c5<>8
A kite originating from BOX 5; r1c94 and an
X-Wing on 4 in row 16; r3c8<>4 which solves it. |
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Clement
Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania
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| Posted: Sun Aug 19, 2012 10:27 am Post subject: Daily Telegraph Diabolical Fri, 17-Aug-2012 |
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| In my above submission I meant; A kite on 4 originating from BOX 5; r1c9<>4. |
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tlanglet
Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills
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| Posted: Sun Aug 19, 2012 12:11 pm Post subject: |
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Clement,
Your first xy-wing becomes a one-stepper with a simple pincer transport such as:
If the pincer at r1c1=2, then r6c1<>2, then r4c2=2 ==> -2r4c6 to complete the puzzle.
As a chain this extended xy-wing can be notated as
(2=4)r3c6-(4=6)r1c5-(6=2)r1c1-2r6c1=2r4c2; -2r1c4, r3c12, r4c6
Ted |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Sun Aug 19, 2012 3:58 pm Post subject: |
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In the XY-Wing 462, the 2 in r3c6 can be transported to r4c2 for a one-stepper.
No one mentioned the 26 W-Wing in boxes 15, also a one-stepper, which was the first move I noticed.
Ted: up with the roosters? |
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tlanglet
Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills
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| Posted: Sun Aug 19, 2012 4:12 pm Post subject: |
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| Marty R. wrote: |
Ted: up with the roosters? |
...... or party till the sun comes up 
Ted |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Sun Aug 19, 2012 4:39 pm Post subject: |
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| tlanglet wrote: |
...... or party till the sun comes up
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Sounds like fun, but I'm too old for that stuff.  |
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Clement
Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania
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| Posted: Sun Aug 19, 2012 5:08 pm Post subject: Daily Telegraph Diabolical Fri, 17-Aug-2012 |
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tlanglet and Marty
Thanks for showing me a single steper solution. Sometimes they are difficult to spot. A Dual Cell Forcing Chain as pointed out by tlanglet is one of the examples e.g whether r1c1 is 2 or 6; r4c6<>2 is actually a single steper. |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Sun Aug 19, 2012 8:16 pm Post subject: |
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| Quote: | | A Dual Cell Forcing Chain as pointed out by tlanglet is one of the examples e.g whether r1c1 is 2 or 6; r4c6<>2 is actually a single steper. |
Clement,
That's not really a Forcing Chain, it's a pincer transport. The XY-Wing pattern has already established that r1c1 is a pincer on 2. If it's a 2, then r4c2 must be 2. This cell now replaces r1c1 as a pincer and works with the other pincer at r3c6 to eliminate the 2 from r4c6.
A transport can be used with any pincer, regardless of how the pincer was established, e.g, XY-, W-, M-Wings and coloring. If a pincer can prove the same value in another cell, then that cell can be used as a pincer to replace the cell that proved it. |
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Clement
Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania
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| Posted: Sun Aug 19, 2012 10:34 pm Post subject: Daily Telegraph Diabolical Fri, 17-Aug-2012 |
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Marty
Noted. |
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ronk
Joined: 07 May 2006
Posts: 398
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| Posted: Mon Aug 20, 2012 12:28 am Post subject: |
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| Marty R. wrote: | | That's not really a Forcing Chain, it's a pincer transport. |
Are you saying that rather than seeing it as a chain, you see it as a pattern? If so, why should either POV be more correct than the other? |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Mon Aug 20, 2012 1:48 am Post subject: |
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| ronk wrote: | | Marty R. wrote: | | That's not really a Forcing Chain, it's a pincer transport. |
Are you saying that rather than seeing it as a chain, you see it as a pattern? If so, why should either POV be more correct than the other? |
I'm not much of a Sudoku thinker or theoretician, just a mechanic. In my little world, a Forcing Chain (Double Implication Chain) is a trial-and-error technique where one goes on a fishing expedition starting with a bivalue cell or similar either/or situation, whereas Pincer Transport is a perfectly legitimate, unquestioned, respected technique used by players who wouldn't consider the thought of using a Forcing Chain in the way I view it.
So my answer to the question is that Pincer Transport is more "correct" than a Forcing Chain, given that "correct'", like beauty, is in the eye of the beholder. |
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Clement
Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania
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| Posted: Mon Aug 20, 2012 6:52 am Post subject: Daily Telegraph Diabolical Fri, 17-Aug-2012 |
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Marty
I do not prescribe to that reasoning. Forcing Chains are just extensions of chain strategies like XY-Chains. Forcing means a cell or unit contains certain numbers which force the removal of numbers to the target cell through different routes. An xy-wing is the shortest Dual Cell Forcing Chain and an xyz -wing is the shortest Triple Cell Forcing Chain.
Therefore, forcing chains are correct and logical like other strategies as in our example here the contents remaining in r1c1 force the removal of 2 in r4c6 whichever route you take. |
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ronk
Joined: 07 May 2006
Posts: 398
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| Posted: Mon Aug 20, 2012 1:02 pm Post subject: |
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| Marty R. wrote: | | In my little world, a Forcing Chain (Double Implication Chain) is a trial-and-error technique where one goes on a fishing expedition starting with a bivalue cell or .... |
I was referring to "what it is" as opposed to "how it's found", but isn't that the way most players find the xy-wing? |
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arkietech
Joined: 31 Jul 2008
Posts: 1834
Location: Northwest Arkansas USA
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| Posted: Mon Aug 20, 2012 2:08 pm Post subject: |
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| ronk wrote: | | Marty R. wrote: | | In my little world, a Forcing Chain (Double Implication Chain) is a trial-and-error technique where one goes on a fishing expedition starting with a bivalue cell or .... |
I was referring to "what it is" as opposed to "how it's found", but isn't that the way most players find the xy-wing? |
I look for 3 bivalue cells with values forming a set of 3  |
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Marty R.
Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
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| Posted: Mon Aug 20, 2012 3:30 pm Post subject: |
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We may have different definitions of Forcing Chains. I described above what it means to me.
I suppose in searching for a pattern there is an element of trial-and-error, just looking around to see what one can find. But once you find that wing, UR, kite, or established pattern, you can confidently proceed to make eliminations without testing to make sure they're OK.
That's a lot different from my concept of a Forcing Chain, even if an XY-Wing is one by official definition. |
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ronk
Joined: 07 May 2006
Posts: 398
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| Posted: Tue Aug 21, 2012 12:45 am Post subject: |
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| Marty R. wrote: | | We may have different definitions of Forcing Chains. I described above what it means to me. |
I've never used the forcing chain term, and don't presume to know what anyone else means by it. However, I do know that chaining strong inferences is possible without assuming any candidate to be true (or false), which is the hallmark of trial-and-error IMO. |
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Luke451
Joined: 20 Apr 2008
Posts: 310
Location: Southern Northern California
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| Posted: Tue Aug 21, 2012 4:18 am Post subject: Re: Daily Telegraph Diabolical Fri, 17-Aug-2012 |
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| Clement wrote: | | I do not prescribe to that reasoning. Forcing Chains are just extensions of chain strategies like XY-Chains. |
Rather than "Forcing Chains," perhaps the better term for chain strategies would be AIC (Alternating Inference Chain.) It describes the pattern under consideration with no ambiguity whatsoever.
Best of all, there can be no question as to whether an AIC is a logical, non T&E procedure. Patterns are great, I love 'em, but we should never lose sight of why they all actually work. |
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