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Aug 3 VH
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nataraj



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

PostPosted: Fri Aug 03, 2007 1:21 pm    Post subject: Aug 3 VH Reply with quote

Hello everybody. This is my first time here, so pls bear with me ...

After smooth sailing I got stuck at this point:

Code:
2   8  1 | 5  379 4 | 6 379 379
5   7  3 | 29 129 6 | 8 4   19
6   4  9 | 37 378 18| 5 2   137
----------------------------
7   13 6 | 8  123 12| 9 5   4
19  5  8 | 4  19  7 | 3 6   2
4   39 2 | 39 6   5 | 7 1   8
----------------------------
89  6  5 | 27 4   28| 1 379 379
3   2  7 | 1  5   9 | 4 8   6
189 19 4 | 6  78  3 | 2 79  5


only way I found to solve this is a XY chain (12-28-89-91) eliminating 1 from r4c2. I don't particularly like forced chains so is there a simpler way?

best regards
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Johan



Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium

PostPosted: Fri Aug 03, 2007 2:10 pm    Post subject: Reply with quote

nataraj,

That one step move with an xy-chain solves the puzzle completely. But if you're looking for something diffirent, there is also an xy-wing and a xyz-wing available.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Fri Aug 03, 2007 2:44 pm    Post subject: Reply with quote

I see an xyz wing for 129 in R2C5, R2C4 and R5C5 that gets rid of the 9 in R1C5.
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Fri Aug 03, 2007 2:54 pm    Post subject: Reply with quote

P.S.

Nataraj: I'm probably missing something obvious here - but how did you solve the 19's in R8?
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nataraj



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

PostPosted: Fri Aug 03, 2007 2:57 pm    Post subject: thx Reply with quote

thank you Johan and cgordon!
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nataraj



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

PostPosted: Fri Aug 03, 2007 3:15 pm    Post subject: @cgordon Reply with quote

sorry I don't remember how I did it because I'm a pencil and paper solver so once the puzzle is finished there is no traceback.

I remember I realized the naked 6 in r2c6 rather late. other than that I cant see a 9 in my PMs in C6.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Fri Aug 03, 2007 3:48 pm    Post subject: Reply with quote

I couldn't find any XY- or XYZ-Wings, but the one XY-Chain solved it, albeit I think I had a somewhat different position from the one posted.
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS

PostPosted: Fri Aug 03, 2007 5:46 pm    Post subject: Aug 3 VH Reply with quote

I found the xyz-wing mentioned by cgordon, removing 9 from R1C5.
Then a four step xy-chain from R4C2 to R1C5, which eliminated the 3 in R4C5 and solved the puzzle.

Thanks for the tips.

Earl
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Fri Aug 03, 2007 5:55 pm    Post subject: Reply with quote

Quote:
but how did you solve the 19's in R8?


I see it now Nataraj ! There was a naked pair of 9s in row 8 leaving a single 9 in col 6. Therefore my xyz for 129 (R2C5 pivot) was OK.
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Bluewing



Joined: 03 Aug 2007
Posts: 1

PostPosted: Fri Aug 03, 2007 5:55 pm    Post subject: Reply with quote

7's Swordfish Rows 1,3 &7 eliminates the 7 in r9c8
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shoeless



Joined: 03 Aug 2007
Posts: 13

PostPosted: Fri Aug 03, 2007 6:34 pm    Post subject: Reply with quote

Ok...I've been staring at this for a while, but I'm obviously missing something. I don't fully get XY chains, but XY and XYZ wings make sense to me. In any case, I solved the puzzle to this point.

Code:
+----------+-----------+---------+
| 2   8  1 | 5  37  4  | 6 37 9  |
| 5   7  3 | 29 29  6  | 8 4  1  |
| 6   4  9 | 37 18  18 | 5 2  37 |
+----------+-----------+---------+
| 7   13 6 | 8  123 12 | 9 5  4  |
| 19  5  8 | 4  19  7  | 3 6  2  |
| 4   39 2 | 39 6   5  | 7 1  8  |
+----------+-----------+---------+
| 89  6  5 | 27 4   28 | 1 39 37 |
| 3   2  7 | 1  5   9  | 4 8  6  |
| 189 19 4 | 6  78  3  | 2 79 5  |
+----------+-----------+---------+


Not sure where to go from there...If I hit the Hint button I get a 2 in r4c6, but I don't know why. Anyone wanna help a newbie?

Thanks in advance Smile
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Fri Aug 03, 2007 7:00 pm    Post subject: Reply with quote

Quote:
7's Swordfish Rows 1,3 &7 eliminates the 7 in r9c8


Could you run that one by me? I don't know anything about Swordfish - in fact I can't remember them coming up in previous posts (at least in the last 4 months).
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Steve R



Joined: 24 Oct 2005
Posts: 289
Location: Birmingham, England

PostPosted: Fri Aug 03, 2007 9:02 pm    Post subject: Reply with quote

Welcome shoeless!

You can eliminate 2 from r4c5 using the xy-wing pivoted on (19) in r5c5 with pincers r2c5 and r4c6.

Steve
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nataraj



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

PostPosted: Fri Aug 03, 2007 9:06 pm    Post subject: Reply with quote

shoeless,

you are stuck at about the same point I was. The XY chain works as follows:

we are going to show that r4c2 cannot be 1.

if r5c1 = 1 then r4c2 cannot be 1 (both in same box)
if r5c1 = 9 (the other possibility) then a chain of inferences is set in motion:

r5c1=9 => r7c1<9>r7c1=8
r7c1=8 => r7c6<8>r7c6=2
r7c6=2 => r4c6<2>r4c6=1

but if r4c6=1 then r4c2<>1

so no matter which value r5c1 assumes, r4c2 can never be 1.
The rest is simple elimination.

Like in a XY wing, the two cells at both ends of a chain contain the same candidate "1" and therefore eliminate "1" from all cells they see.

why it says 2 at r4c6 - beats me. 2 is correct of course but becomes solved only after a few steps.
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nataraj



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

PostPosted: Fri Aug 03, 2007 9:08 pm    Post subject: Reply with quote

thx, steve. I did it again - failed to see the xy wing
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Fri Aug 03, 2007 9:14 pm    Post subject: Reply with quote

cgordon,

I'm sorry to say that there is no Swordfish on 7 in this puzzle.

X-Wing, Swordfish and Jellyfish are closely related and are explained here:
http://www.sudocue.net/guide.php#XWing

For me, the puzzle yielded to a single XY-Chain that eliminates <2> from R7C6. Seems there are lots of XY-Chains in this one!
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Fri Aug 03, 2007 9:20 pm    Post subject: Reply with quote

Quote:
why it says 2 at r4c6 - beats me. 2 is correct of course but becomes solved only after a few steps.


It probably says that because XY-Wings is one of the techniques built into these puzzles, whereas XY-Chains are not.
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nataraj



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

PostPosted: Fri Aug 03, 2007 9:28 pm    Post subject: Reply with quote

Quote:
It probably says that because XY-Wings is one of the techniques built into these puzzles, whereas XY-Chains are not.


Come to think of it, the program maybe cannot give "negative" hints on elimination but only "positive" hints.
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George Woods



Joined: 28 Mar 2006
Posts: 304
Location: Dorset UK

PostPosted: Fri Aug 03, 2007 10:38 pm    Post subject: A Solution that I Hate Reply with quote

In solving this I found a solution that I am almost ashamed of

The 379s in Boxes 3 and 9 might easily bea DR either by removing either 3 7 or 9 from all.

So for badness postulate that r9c8 is 7 - it is not difficult to see that this makes r1c5 7 and we have the dreaded DR in 39 So r9c8 must be 9 and hence a solution

I so hated this solution that I had to look for another and finally settled on the kind of xyz wing pivoting on 123 at r4c5. Hence I almost got double value from the puzzle!
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Sat Aug 04, 2007 12:21 am    Post subject: Reply with quote

Quote:
The 379s in Boxes 3 and 9 might easily bea DR either by removing either 3 7 or 9 from all.

So for badness postulate that r9c8 is 7 - it is not difficult to see that this makes r1c5 7 and we have the dreaded DR in 39 So r9c8 must be 9 and hence a solution


George, I can't follow the line of logic. If r9c8=7, then r9c5=8. The resulting 37 pair in box 2 forces r1c5=9.

Code:
2   8  1 | 5  379 4 | 6 379 379
5   7  3 | 29 129 6 | 8 4   19
6   4  9 | 37 378 18| 5 2   137
----------------------------
7   13 6 | 8  123 12| 9 5   4
19  5  8 | 4  19  7 | 3 6   2
4   39 2 | 39 6   5 | 7 1   8
----------------------------
89  6  5 | 27 4   28| 1 379 379
3   2  7 | 1  5   9 | 4 8   6
189 19 4 | 6  78  3 | 2 79  5
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