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Oct 2 vh

 
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Thu Oct 02, 2008 6:42 am    Post subject: Oct 2 vh Reply with quote

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        |
+--------------------------+--------------------------+--------------------------+


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

PostPosted: Thu Oct 02, 2008 9:03 am    Post subject: Reply with quote

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

PostPosted: Thu Oct 02, 2008 10:30 am    Post subject: Reply with quote

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
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tlanglet



Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills

PostPosted: Thu Oct 02, 2008 12:33 pm    Post subject: Reply with quote

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

PostPosted: Thu Oct 02, 2008 1:39 pm    Post subject: Reply with quote

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
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eddieg



Joined: 12 Jan 2006
Posts: 47
Location: San Diego, CA USA

PostPosted: Thu Oct 02, 2008 2:35 pm    Post subject: Puzzles getting easier -or- Puzzlers getting smarter Reply with quote

Maybe some of both?
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nataraj



Joined: 03 Aug 2007
Posts: 1048
Location: near Vienna, Austria

PostPosted: Thu Oct 02, 2008 2:58 pm    Post subject: Reply with quote

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

PostPosted: Thu Oct 02, 2008 3:39 pm    Post subject: Daily Sudoku: Thu 2-Oct-2008 VH Reply with quote

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

PostPosted: Thu Oct 02, 2008 3:53 pm    Post subject: Reply with quote

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

PostPosted: Thu Oct 02, 2008 5:20 pm    Post subject: Reply with quote

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 ? Smile

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

PostPosted: Thu Oct 02, 2008 8:19 pm    Post subject: A Variant of an Xy Wing? Reply with quote

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

PostPosted: Thu Oct 02, 2008 11:33 pm    Post subject: Reply with quote

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

PostPosted: Fri Oct 03, 2008 12:28 am    Post subject: Reply with quote

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

PostPosted: Fri Oct 03, 2008 7:53 pm    Post subject: Reply with quote

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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