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nataraj
Joined: 03 Aug 2007 Posts: 1048 Location: near Vienna, Austria
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Posted: Thu Oct 02, 2008 6:42 am Post subject: Oct 2 vh |
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I had a very good time solving this one (with a twist at the end)
After basics, there is a skyscraper (6) in rows 4 and 8, plus an x-wing (4) in rows 6 and 8.
After that,
Code: |
+--------------------------+--------------------------+--------------------------+
| 4 13 5 | 7 6 8 | 13 9 2 |
| 6 2 38 | 1 9 5 | 38 7 4 |
| 79 18 79 | 4 2 3 | 5 16 68 |
+--------------------------+--------------------------+--------------------------+
| 8 4-6 ! 1 | 2 3 7 | 46 5 9 |
| 37# 36* 237 | 9 5 4 | 18 12-6 68 |
| 5 9 24 | 6 8 1 | 7 24 3 |
+--------------------------+--------------------------+--------------------------+
| 13# 348 368 | 5 14 9 | 2 36* 7 |
| 19 7 69 | 3 14 2 | 46 8 5 |
| 2 5 34 | 8 7 6 | 9 34 1 |
+--------------------------+--------------------------+--------------------------+
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a w-wing (6)r5c2=r7c8,
which not only eliminates 6 from r5c8 directly, but serves as a new strong link,
which allows to eliminate 6 from r4c2 as well:
(6) r4c2-r5c2=[w-wing]=r7c8-r8c7=r4c7-r4c2
P.S. I see that there is also a xy-wing (14-13-34 boxes 7 and 8) that has the same effect (r4c2=4). |
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Asellus
Joined: 05 Jun 2007 Posts: 865 Location: Sonoma County, CA, USA
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Posted: Thu Oct 02, 2008 9:03 am Post subject: |
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Not only does that 134 XY Wing have the same effect, it is all you need from the get-go to solve the puzzle. |
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nataraj
Joined: 03 Aug 2007 Posts: 1048 Location: near Vienna, Austria
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Posted: Thu Oct 02, 2008 10:30 am Post subject: |
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Asellus wrote: | Not only does that 134 XY Wing have the same effect, it is all you need from the get-go to solve the puzzle. |
Boy, am I glad I did not see the xy-wing. Would have completely ruined my day ![Cool](images/smiles/icon_cool.gif) |
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tlanglet
Joined: 17 Oct 2007 Posts: 2468 Location: Northern California Foothills
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Posted: Thu Oct 02, 2008 12:33 pm Post subject: |
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Sorry to say that I saw the xy-wing <134> one-punch knockout. However I did the puzzle a second time and ignored it; three steps were required.
Ted |
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arkietech
Joined: 31 Jul 2008 Posts: 1834 Location: Northwest Arkansas USA
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Posted: Thu Oct 02, 2008 1:39 pm Post subject: |
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Code: | +--------------------------+--------------------------+--------------------------+
| 4 13 5 | 7 6 8 | 13 9 2 |
| 6 2 38 | 1 9 5 | 38 7 4 |
| 79 18 79 | 4 2 3 | 5 16 68 |
+--------------------------+--------------------------+--------------------------+
| 8 4-6 1 | 2 3 7 |B46 5 9 |
|a37# *36 237 | 9 5 4 | 18 12-6 68 |
| 5 9 24 | 6 8 1 | 7 24 3 |
+--------------------------+--------------------------+--------------------------+
|A13# 348 368 | 5 14 9 | 2 *36 7 |
| 19 7 69 | 3 14 2 |b46 8 5 |
| 2 5 34 | 8 7 6 | 9 34 1 |
+--------------------------+--------------------------+--------------------------+
a w-wing
ab w-wing |
Did I get it right? Is it one pattern or two? What do you call it?
W-wings sure come hard to me. ![Confused](images/smiles/icon_confused.gif) |
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eddieg
Joined: 12 Jan 2006 Posts: 47 Location: San Diego, CA USA
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Posted: Thu Oct 02, 2008 2:35 pm Post subject: Puzzles getting easier -or- Puzzlers getting smarter |
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Maybe some of both? |
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nataraj
Joined: 03 Aug 2007 Posts: 1048 Location: near Vienna, Austria
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Posted: Thu Oct 02, 2008 2:58 pm Post subject: |
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arkietech,
the pattern *-a-A-* in your grid is a w-wing.
Characteristics:
"the pincers": two identical bi-value cells (r5c2,r7c8 have two candidates 3 and 6) that do not share a house.
The "wing": both cells "see" the ends of a strong link in one of the two candidates (in this case the candidate is 3, the strong link is between r5c1 and r7c1)
The victim: Every cell that sees both pincers cannot contain the other candidate (6), so r5c8<>6.
The pincers act as a strong link (at least one of them must be 6), so we can construct another elimination altogether (not a w-wing), that gets rid of the 6 in r4c2. This other elimination is shown in my drawing. I gave the "shorthand" notation for this AIC
(6) r4c2-r5c2=[w-wing]=r7c8-r8c7=r4c7-r4c2
, what it means is:
if r5c2 is not 6 then (because of the w-wing) r7c8 is 6.
But then r8c7 is not 6, then r4c7 is 6.
r4c2 sees both r5c2 and r4c7 and therefore cannot be 6 |
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Clement
Joined: 24 Apr 2006 Posts: 1111 Location: Dar es Salaam Tanzania
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Posted: Thu Oct 02, 2008 3:39 pm Post subject: Daily Sudoku: Thu 2-Oct-2008 VH |
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XY-Wing 134 Pivot {1,3}r7c1 with Pincers in r9c3{3,4} and r7c5{1,4} eliminating the 4's in r7c23 leaving 4 as the only candidate in r4c2. This solves the puzzle. |
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Marty R.
Joined: 12 Feb 2006 Posts: 5770 Location: Rochester, NY, USA
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Posted: Thu Oct 02, 2008 3:53 pm Post subject: |
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Quote: | The pincers act as a strong link (at least one of them must be 6), so we can construct another elimination altogether (not a w-wing), that gets rid of the 6 in r4c2. This other elimination is shown in my drawing. I gave the "shorthand" notation for this AIC
(6) r4c2-r5c2=[w-wing]=r7c8-r8c7=r4c7-r4c2
, what it means is:
if r5c2 is not 6 then (because of the w-wing) r7c8 is 6.
But then r8c7 is not 6, then r4c7 is 6.
r4c2 sees both r5c2 and r4c7 and therefore cannot be 6 |
Hate to be critical, old buddy, but isn't this a little overkill for what is a simple case of pincer coloring, or transport, if you will? |
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nataraj
Joined: 03 Aug 2007 Posts: 1048 Location: near Vienna, Austria
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Posted: Thu Oct 02, 2008 5:20 pm Post subject: |
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Marty R. wrote: |
Hate to be critical, old buddy, but isn't this a little overkill for what is a simple case of pincer coloring, or transport, if you will? |
Total overkill, I agree, for what is essentially a one xy-wing puzzle.
But that wasn't the criticism, was it ?
Overkill for "what is a simple case of ..." ?
Don't know. "pincer coloring" or "transport" might not be so simple. I don't mind typing a few more lines and spell out the logic. One doesn't come across a w-wing with pincer coloring every day ... Good thing you answered archietech's "What do you call it" question... I missed that one completely. |
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George Woods
Joined: 28 Mar 2006 Posts: 304 Location: Dorset UK
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Posted: Thu Oct 02, 2008 8:19 pm Post subject: A Variant of an Xy Wing? |
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The simple solution is the XY wing in boxes 6 & 7 BUT I used a solution albeit more complex but to me is interesting.
Looking for an XY I saw the 13 (box1) and 36(Box 4) and looking for a 16 to complete the XY I noticed the one in box3. No good BUT the 68s in col 9 connect the 36 to the 16 to give an XY 13 36 68 86 61 chain, eliminating 1 from r1c7 to give an easy solution.
I presume XY chains are "inferior" to XY Wings, But it didn't need the 68 link to be a naked pair (allowing a simple XY chain). Had the 6's been strongly linked in col 7 the same logic would have worked albeit no simple XY chain. Has this variant of an XY chain got a name?
Incidentally I often find recently , and so it was today, the the ranking (very Hard) does not appear on th print out. By using draw/play , and the tab "Today" followed by print, I get the grading! |
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Asellus
Joined: 05 Jun 2007 Posts: 865 Location: Sonoma County, CA, USA
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Posted: Thu Oct 02, 2008 11:33 pm Post subject: |
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George Woods wrote: | I presume XY chains are "inferior" to XY Wings, But it didn't need the 68 link to be a naked pair (allowing a simple XY chain). Had the 6's been strongly linked in col 7 the same logic would have worked albeit no simple XY chain. Has this variant of an XY chain got a name? |
Some folks call your XY Chain an "Extended XY-Wing" since it is an XY-Wing "extended" by the locked pair. You are correct that an "extension" by the conjugate <6>s alone is equivalent and I would consider that to be an Extended XY-Wing as well.
I am not among those who consider XY Chains "inferior". But, I also don't consider AICs inferior and would call the short chain with the conjugate <6>s just a simple Alternate Implication Chain (AIC). |
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keith
Joined: 19 Sep 2005 Posts: 3355 Location: near Detroit, Michigan, USA
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Posted: Fri Oct 03, 2008 12:28 am Post subject: |
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I am late to the discussion, and I have not read all the posts in detail. This one took not much time. After filling in the singles, and only candidates in those cells where there are two:
Code: | +----------+----------+----------+
| 4 13 5 | 7 6 8 | 13 9 2 |
| 6 2 38 | 1 9 5 | 38 7 4 |
| 18 | 4 2 3 | 5 16 68 |
+----------+----------+----------+
| 8 46 1 | 2 3 7 | 46 5 9 |
| 37 36 | 9 5 4 | 68 |
| 5 9 24 | 6 8 1 | 7 24 3 |
+----------+----------+----------+
| 13 (-4) | 5 14 9 | 7 |
| 19 7 | 3 14 2 | 46 8 5 |
| 2 5 34 | 8 7 6 | 9 34 1 |
+----------+----------+----------+ | No pairs, no line/column intersections. There is an XY-wing <134> in B7R7. In C2, R7 is not <4>, R4 must be <4>, and the puzzle is solved.
Keith
Last edited by keith on Fri Oct 03, 2008 10:09 pm; edited 1 time in total |
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DennyOR
Joined: 12 Sep 2007 Posts: 33 Location: Portland, Oregon
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Posted: Fri Oct 03, 2008 7:53 pm Post subject: |
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My solution was the xy chain 34-46-69-91-13.
Since I look for xy chains instead of xy-wings, I'm as likely to find a long chain as a 3-member chain (wing). Flitting around from one linked pair to the next to see if I can find any matched ends that eliminate numbers is my sudoku fun time. I find the rest of process of solving a sudoku to be tedious (but still satisfying). |
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