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recommended: today's nightmare

 
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nataraj



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

PostPosted: Thu Dec 13, 2007 9:10 am    Post subject: recommended: today's nightmare Reply with quote

Today's Daily Nightmare once more turned out to be a very satisfying puzzle.

xy-wing and x-wing got me here:

Code:

+--------------------------+--------------------------+--------------------------+
| 58      135     18       | 24      359     7        | 89      6       24       |
| 679     37      2        | 46      36      8        | 1       5       49       |
| 4       59      689      | 1       569     25       | 7       3       28       |
+--------------------------+--------------------------+--------------------------+
| 2       6       3        | 8       1       9        | 4       7       5        |
| 1       457     47       | 57      2       3        | 89      89      6        |
| 58      579     789      | 57      4       6        | 3       2       1        |
+--------------------------+--------------------------+--------------------------+
| 3       8       19       | 26      56      4        | 25      19      7        |
| 79      2       5        | 3       78      1        | 6       4       89       |
| 67      147     1467     | 9       78      25       | 25      18      3        |
+--------------------------+--------------------------+--------------------------+


I see at least two different solution paths now:
A) potential DP (57) r56c24 => r5c2=4 or r6c2=9, both lead to r5c4=5.
B) xy-chain *): (9)r7c3 ... [useless xy-wing 91-18-89 + transport to] ... (9)r5c8 makes r7c8=1

edit: *) xy-chain ? or w-wing ? M-wing ? wingding ? Laughing
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Earl



Joined: 30 May 2007
Posts: 668
Location: Victoria, KS

PostPosted: Thu Dec 13, 2007 5:59 pm    Post subject: Nightmare Reply with quote

There is a w-wing 18 apparently elliminating nothing, but if you color the lower pincer 8 to R3C9 that makes R1C7 = 9 and the puzzle is solved.

Earl
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nataraj



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

PostPosted: Thu Dec 13, 2007 6:41 pm    Post subject: Reply with quote

I'll add that to the list of powerful chains based on apperently useless wings.

So far, we have:

(9)r7c3 19-18-89-89-89 (9)r5c8 ; r7c8=1 (nataraj's)
(8)r1c3 18-19-19-18-89-49-24-28 (8)r3c9; R1C7 = 9 (Earl's)

If we start with the same useless w-wing but continue up and left we get to r5c7 with the same result

(8)r1c3 18-19-19-18-89-89 (8)r5c7 ; r1c7=9 (Earl's II)

and here's one more, it removes 1 from r7c3. It looks like a normal xy-wing but with an extension cord added in the middle:

(1)r1c3 18-89-89-89-19 (1)r7c8 ; r7c3=9
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Thu Dec 13, 2007 11:11 pm    Post subject: Reply with quote

nataraj wrote:
I'll add that to the list of powerful chains based on apparently useless wings.



Flightless wings?

Keith
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TKiel



Joined: 22 Feb 2006
Posts: 292
Location: Kalamazoo, MI

PostPosted: Fri Dec 14, 2007 12:32 am    Post subject: Reply with quote

Ostrich?
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Asellus



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

PostPosted: Fri Dec 14, 2007 5:55 am    Post subject: Reply with quote

Some might have noticed I have been intrigued recently with otherwise useless X-Wings involved with overlapping strong links. In this case, I saw the <4> X-Wing in Boxes 2 and 3 with the overlapping <2> strong link in r1. Together with the Box 2 strongly linked <2>s and several related bivalues, I thought: Medusa! I usually don't resort to Medusa so soon. But, this seemed so promising:
Code:
+--------------+-----------------+--------------+
| 58  135 18   | 2r4g  359r 7    | 8r9g 6  2g4r |
| 679 37  2    | 4r6g  3-6  8    | 1    5  4g9r |
| 4   59  689  | 1    -569g 2g5r | 7    3  2r8g |
+--------------+-----------------+--------------+
| 2   6   3    | 8     1    9    | 4    7  5    |
| 1   457 47   | 57    2    3    | 89   89 6    |
| 58  579 789  | 57    4    6    | 3    2  1    |
+--------------+-----------------+--------------+
| 3   8   19   | 26    56   4    | 25   19 7    |
| 79  2   5    | 3     78   1    | 6    4  89   |
| 67  147 1467 | 9     78   25   | 25   18 3    |
+--------------+-----------------+--------------+

Very easily, <5> is eliminated from r3c5. (It contains a green <9> and sees a red <5>.) This makes the <6> in r3c5 red, eliminating <6> from r2c5 and solving the puzzle.
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nataraj



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

PostPosted: Fri Dec 14, 2007 6:40 am    Post subject: Reply with quote

TKiel wrote:
Ostrich?


Laughing That's it! Let's call it ostrich wing (or O-wing for short). Nobody's going to believe this... Laughing
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Fri Dec 14, 2007 7:29 am    Post subject: Reply with quote

are we "o-wing" you anything for this?
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nataraj



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

PostPosted: Fri Dec 14, 2007 7:42 am    Post subject: Reply with quote

it was a collaboration - but "ostrich" was suggested by Tracy, to be sure.


I can think of many more uses for the name. Take those solution methods, for example, that leave me with my mouth open ... :-O oooohhh - wing!
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