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LA Times / Freep 4 April, 2008

 
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keith



Joined: 19 Sep 2005
Posts: 3179
Location: near Detroit, Michigan, USA

PostPosted: Sat Apr 05, 2008 11:43 am    Post subject: LA Times / Freep 4 April, 2008 Reply with quote

Any creative ideas?
Code:
Puzzle: FP040408
+-------+-------+-------+
| 2 . . | . 4 . | . . 5 |
| . . . | 5 . . | . 7 . |
| . 5 . | . . 1 | . 3 . |
+-------+-------+-------+
| . . 7 | 8 1 . | 6 . . |
| . . 9 | . 5 . | 2 . . |
| . . 1 | . 3 2 | 7 . . |
+-------+-------+-------+
| . 9 . | 4 . . | . 1 . |
| . 6 . | . . 5 | . . . |
| 8 . . | . 6 . | . . 7 |
+-------+-------+-------+

Keith
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Steve R



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

PostPosted: Sat Apr 05, 2008 12:57 pm    Post subject: Reply with quote

Code:
+----------------------------------------+
| 2    7   8   | 3   4   9  | 1   6   5  |
| 1349 134 346 | 5   28  68 | 48  7   29 |
| 49   5   46  | 267 278 1  | 48  3   29 |
------------------------------------------
| 5    2   7   | 8   1   4  | 6   9   3  |
| 34   348 9   | 67  5   67 | 2   48  1  |
| 6    48  1   | 9   3   2  | 7   5   48 |
------------------------------------------
| 37   9   23  | 4   278 78 | 5   1   6  |
| 17   6   34  | 17  9   5  | 3   248 48 |
| 8    14  5   | 12  6   3  | 9   24  7  |
+----------------------------------------+


You can use a generalised XY-wing with pivot r78c1. These two cells must contain 1 or 3, just like a bivalent cell (13). The pincers r5c1 and r9c2 then eliminate 4 from r56c2.

Steve
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keith



Joined: 19 Sep 2005
Posts: 3179
Location: near Detroit, Michigan, USA

PostPosted: Sat Apr 05, 2008 1:27 pm    Post subject: Reply with quote

Really?

It seems correct, but I do not recall seeing this before!

In Steve's grid there is a skyscraper that takes out <4> in R8C9, but that does not solve the puzzle. It gets you here:
Code:
+----------------+----------------+----------------+
| 2    7    8    | 3    4    9    | 1    6    5    |
| 1349 134  346  | 5    28   68   | 48   7    29   |
| 49   5    46   | 267  278  1    | 48   3    29   |
+----------------+----------------+----------------+
| 5    2    7    | 8    1    4    | 6    9    3    |
|-34   34#  9    | 67   5    67   | 2    8    1    |
| 6    8    1    | 9    3    2    | 7    5    4    |
+----------------+----------------+----------------+
| 37#  9    23   | 4    278  78   | 5    1    6    |
| 17@  6    24   | 17   9    5    | 3    24   8    |
| 8    14@  5    | 12   6    3    | 9    24   7    |
+----------------+----------------+----------------+

Can I make this similar argument: Question
R8C1 and R9C2 , @, must contain one of <47>.
Either way, one of the pincer cells # is <3>, and we can take out <3> in R5C1. Surprised

(I do see that there are short chains that solve R5C12. I tried Medusa coloring, starting with R9C2, but there are not strong links for <3> or <4> in C12 that allow you to get to the <34> pair in B4.)

Keith


Last edited by keith on Sat Apr 05, 2008 5:21 pm; edited 1 time in total
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Victor



Joined: 29 Sep 2005
Posts: 207
Location: NI

PostPosted: Sat Apr 05, 2008 4:48 pm    Post subject: Reply with quote

And, not as exciting as Steve's stuff, the ER based on r9 takes out the 4 in r6c2, exposing a type 4 in 34s in r2c12. Same effect as Keith's skys, I guess - still a little work to do.
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Marty R.



Joined: 12 Feb 2006
Posts: 5166
Location: Rochester, NY, USA

PostPosted: Sat Apr 05, 2008 5:11 pm    Post subject: Reply with quote

Quote:
I tried Medusa coloring, starting with R9C2, but there are not strong links for <3> or <4> in C12 that allow you to get to the <34> pair in B4

Keith, Medusa will color the 1 in r2c2 as "A." The 1 and 3 in r2c1 and r2c3, respectively, will be colored "B." Thus the 4 in r2c2 will be "B", eliminating the 3 and exposing a 14 pair in column 2.
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keith



Joined: 19 Sep 2005
Posts: 3179
Location: near Detroit, Michigan, USA

PostPosted: Sat Apr 05, 2008 6:42 pm    Post subject: Reply with quote

Marty R. wrote:
Quote:
I tried Medusa coloring, starting with R9C2, but there are not strong links for <3> or <4> in C12 that allow you to get to the <34> pair in B4

Keith, Medusa will color the 1 in r2c2 as "A." The 1 and 3 in r2c1 and r2c3, respectively, will be colored "B." Thus the 4 in r2c2 will be "B", eliminating the 3 and exposing a 14 pair in column 2.

Marty,

Thanks. I did not take it that far. I confined my search to B47 in the hopes of finding a short chain like Steve did.

Keith
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keith



Joined: 19 Sep 2005
Posts: 3179
Location: near Detroit, Michigan, USA

PostPosted: Sat Apr 05, 2008 10:48 pm    Post subject: Reply with quote

Put in my two cents:

http://www.sudoku.com/boards/viewtopic.php?p=54708#54708

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5166
Location: Rochester, NY, USA

PostPosted: Sun Apr 06, 2008 12:11 am    Post subject: Reply with quote

From that other forum:

Quote:
These turn out to be 4-link XY-chains. As Steve observed, sort of an extended XY-wing.


Ah, but as Steve described it, a "generalized XY-Wing" has more status and, to use a word often seen here, much more elegant than an XY-Chain. Laughing
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tlanglet



Joined: 17 Oct 2007
Posts: 2461
Location: Northern California Foothills

PostPosted: Sun Apr 06, 2008 1:33 am    Post subject: Reply with quote

I used multi-coloring to remove <4> from r5c8, r6c2 & r8c9. If I then use the "generalized XY-wing with pivot r78c1" noted by Steve, the puzzle is completed.

Steve, is your generalized solution a valid technique?

Ted
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keith



Joined: 19 Sep 2005
Posts: 3179
Location: near Detroit, Michigan, USA

PostPosted: Sun Apr 06, 2008 2:29 am    Post subject: Reply with quote

Marty R. wrote:
From that other forum:

Quote:
These turn out to be 4-link XY-chains. As Steve observed, sort of an extended XY-wing.


Ah, but as Steve described it, a "generalized XY-Wing" has more status and, to use a word often seen here, much more elegant than an XY-Chain. Laughing


Marty,

This is new to you?

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5166
Location: Rochester, NY, USA

PostPosted: Sun Apr 06, 2008 3:50 am    Post subject: Reply with quote

Quote:
This is new to you?


Yes, if you mean the generalized XY-Wing, no if you mean XY-Chains.
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