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Jan 30 VH

 
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kragzy



Joined: 01 May 2007
Posts: 112
Location: Australia

PostPosted: Wed Jan 30, 2008 12:08 am    Post subject: Jan 30 VH Reply with quote

I was just thinking the other day that I hadn't seen an XYZ wing for a while, and bingo, today's puzzle needed one. Well, it did for me anyway - I don't do colouring, URs, or skyscrapers unless I have to.

Nice puzzle.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Wed Jan 30, 2008 3:45 am    Post subject: Reply with quote

after basics,
we get more squirrelleys !!! Laughing Laughing Laughing

Code:
17      6       8       | 1579    579     3       | 4       159     2
13      25      9       | 4       8       12      | 6       7       135
137     25      4       | 1579    2579    6       | 13      1359    8
---------------------------------------------------------------------
5       8       6       | 179     379     179     | 137     2       4
2       3       7       | 15      6       4       | 9       8       15
9       4       1       | 8       2357    27      | 37      35      6
---------------------------------------------------------------------
8       17      5       | 6       4       79      | 2       13      139
6       9       3       | 2       1       5       | 8       4       7
4       17      2       | 3       79      8       | 5       6       19



I don't see any xy-chains that break it in one step.
I don't see any xy-wings that break it in one step.
however, I do see a multitude of two step moves.

if you take the xy-wing on {1,3,5} and follow it through, ( the more interesting path IMHO) you will come to

Code:
@17     6       8       | @17    #59      3       | 4      #59      2
13     $25      9       | 4       8       12      | 6       7      $15
@17    $25      4       | $@1579  259     6       | 13      359     8
---------------------------------------------------------------------
5       8       6       | 19      39      17      | 137     2       4
2       3       7       | $15     6       4       | 9       8      $15
9       4       1       | 8      #235     27      | 37     #35      6
---------------------------------------------------------------------
8       7       5       | 6       4       9       | 2       3       3
6       9       3       | 2       1       5       | 8       4       7
4       1       2       | 3       7       8       | 5       6       9


any one of these completes the puzzle...

UR on {1,7} = @ = removes {1,7} in r3c4
coloring on 1 removes 1 in r2c9 and r3c4
xyz-wing {2,5,9} in box 2
--------------- Rolling Eyes -------------------------------- Rolling Eyes --------------------------
these do not complete the puzzle...!

x-wing on 5 = # = removes 5 in r3c58
for you fishermen, there is also a swordfish on 5 = $ = same removals as the x-wing
---------------- Rolling Eyes ------------------------------ Rolling Eyes --------------------------

did someone mention swordfish??? I think I remember reading that somewhere.

and before I get hooked off the stage...there is more Shocked
if you decide to skip the xy-wing on {1,3,5}

you could always color the 1 first...that gets you to here

Code:
17      6       8       | 1579    579     3       | 4       159     2
13      25      9       | 4       8       12      | 6       7      %35
137     25      4       | 579     2579    6       |%13      1359    8
---------------------------------------------------------------------
5       8       6       | 179     379     179     | 137     2       4
2       3       7       | 15      6       4       | 9       8      %15
9       4       1       | 8       2375    27      | 37     35       6
---------------------------------------------------------------------
8       17      5       | 6       4       79      | 2       13      139
6       9       3       | 2       1       5       | 8       4       7
4       17      2       | 3       79      8       | 5       6       19


one xy-wing {1,3,5} present = % = removes 1 from r4c7 and kills it.

no swordfish, no UR, no xyz-wing, no x-wing
many xy-chains.

Norm
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Marty R.



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

PostPosted: Wed Jan 30, 2008 6:23 am    Post subject: Reply with quote

I missed the XY- and XYZ-Wings, but a W-Wing and ER did it for me.
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nataraj



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

PostPosted: Wed Jan 30, 2008 6:52 am    Post subject: Reply with quote

For me, it was
1) a coloring elimination (r2c6=r4c6-r4c7=r5c9) took out 1 in r2c9, which in turn opened an

2) xy-wing 13-35-15 (box 3,6), which [removed 1 from r6c7, giving a naked pair {37} in col 7 and thus] gave r3c7=1 and singles from there
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andras



Joined: 31 Oct 2007
Posts: 56
Location: Mid Wales

PostPosted: Wed Jan 30, 2008 9:36 am    Post subject: Reply with quote

Quite a straightforward one, I thought; xy-wing on 1,3,5 followed shortly after by an x-y-z on 2,5,9.

I do like the fact that there are so many different routes to the answer! Smile

John
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lg161



Joined: 17 Oct 2006
Posts: 12

PostPosted: Wed Jan 30, 2008 9:20 pm    Post subject: jan30 vh Reply with quote

nataraj; pls explain coloring so tha (r2c6=r4c6-r4c7=r5c9) takes out the 1,
(what to the = and - signs mean?) and
andras: where is the xyz wing on [259]?
Thanks a lot.
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Marty R.



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

PostPosted: Wed Jan 30, 2008 10:21 pm    Post subject: Reply with quote

Quote:
andras: where is the xyz wing on [259]?


I'm not andras, but look at the second grid in Norm's post. It's in r3c5, r1c5 and r3c2.

P.S. Welcome to the forum.
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Wed Jan 30, 2008 11:01 pm    Post subject: Re: jan30 vh Reply with quote

lg161 wrote:
nataraj; pls explain coloring so tha (r2c6=r4c6-r4c7=r5c9) takes out the 1,
(what to the = and - signs mean?) and
I'm not nataraj Smile But for a quick answer: in this case it describes a kite elimination.
Code:
 *-----------------------------------------------------------*
 | 17    6     8     | 1579  579   3     | 4     159   2     |
 | 13    125   9     | 4     8    #12    | 6     7    -135   |
 | 137   1257  4     | 1579  2579  6     | 13    1359  8     |
 |-------------------+-------------------+-------------------|
 | 5     8     6     | 179   379  #179   |#137   2     4     |
 | 2     3     7     | 15    6     4     | 9     8    #15    |
 | 9     4     1     | 8     2357  27    | 37    35    6     |
 |-------------------+-------------------+-------------------|
 | 8     17    5     | 6     4     79    | 2     139   139   |
 | 6     9     3     | 2     1     5     | 8     4     7     |
 | 4     17    2     | 3     79    8     | 5     6     19    |
 *-----------------------------------------------------------*

"=" means a strong link. There are only 2 possibilties, either one is true or the other. r2c6=r4c6 here says, if 1 is not in r2c6, then in r4c6 and vice versa.
'-' means a weak link, i.e if one is true, the other is false. E.g. r4c6-r4c7 here says, if 1 is in r4c6, then it cant be in r4c7 and vice versa.

Together you have with r2c6=r4c6-r4c7=r5c9:
Either r2c6=1 or r4c6=1, then r4c7<>1, then r5c9=1.
(If r2c6=1, then also r4c4 and r5c9 could be 1)
Or in the other direction
Either r5c9=1 or r4c7=1, then r4c6<>1, then r2c6=1.

Both say, either r2c6=1 or r5c9=1 or both are 1.
Since r2c9 "sees" both cells, it cannot be 1.

Now you could add another weak and strong link to get
r2c6=r4c6-r4c7=r5c9-r9c9=r9c2
what means either r2c6=1 or r9c2=1 (or both). Thus you could eliminate 1 from r2c2 safely too (i did not apply the 17 pair here, which of course makes this elimination also).


Last edited by ravel on Wed Jan 30, 2008 11:18 pm; edited 1 time in total
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Asellus



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

PostPosted: Wed Jan 30, 2008 11:15 pm    Post subject: Reply with quote

storm_norm,

After that {135} XY Wing, a Skyscraper on <1> in c67 solves it.
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lg161



Joined: 17 Oct 2006
Posts: 12

PostPosted: Wed Jan 30, 2008 11:47 pm    Post subject: jan 30 vh Reply with quote

wow Ravel,
Thank you. I don't know if I will ever see those on my own. But thank your for explaining.
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keith



Joined: 19 Sep 2005
Posts: 3340
Location: near Detroit, Michigan, USA

PostPosted: Thu Jan 31, 2008 2:47 am    Post subject: Re: jan 30 vh Reply with quote

lg161 wrote:
wow Ravel,
Thank you. I don't know if I will ever see those on my own. But thank your for explaining.

Stay around for a week or two and, trust me, you will.

Keith
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nataraj



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

PostPosted: Thu Jan 31, 2008 6:09 pm    Post subject: Re: jan 30 vh Reply with quote

lg161 wrote:
I don't know if I will ever see those on my own.


Hi, lg, and welcome!

I see ravel has already given an excellent explanation (and a rather more understandable one than mine would have been). Good to know that with different timezones, frequent travelling and all that, there are always people up and active in the forum ...

As to seeing the patterns, I don't do it looking at the grid directly, but make little sketches on the paper next to the puzzle, one for each candidate digit. This time, starting at "1", I hit the mother lode immediately. Most of the time this process takes longer, like 5-10 minutes maybe.
The only coloring pattern I see in the grids directly is the x-wing when the two cells are right next to each other (plus of course the other wings, but those are easier to see because one only has to look at bi-value cells)

So, don't worry, most of the "very hard"s here can be solved by xy-wing and simple x-wing, no need for more elaborate patterns (although once you get into them, they are great fun to hunt for)
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ravel



Joined: 21 Apr 2006
Posts: 536

PostPosted: Fri Feb 01, 2008 8:14 am    Post subject: Reply with quote

lg161,

you might want to read this classical introduction to strong links. At least skyscrapers are not harder to spot than x-wings - and they are rather common even in puzzles, that are selected not to need them (like newspaper puzzles or the VH here).

[Added:]Puzzle, that solves with a skyscraper:
Code:
 +-------+-------+-------+
 | . . . | 1 2 3 | . . . |
 | . 4 . | . 5 . | . 6 . |
 | . . . | . . . | . . . |
 +-------+-------+-------+
 | 7 . . | . . . | . . 3 |
 | 4 6 . | . 8 . | . 5 2 |
 | 5 . . | . . . | . . 1 |
 +-------+-------+-------+
 | . . . | . . . | . . . |
 | . 7 . | . 6 . | . 4 . |
 | . . . | 3 9 4 | . . . |
 +-------+-------+-------+ JPF
>>> play online
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