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DB Saturday Puzzle - September 16, 2006

 
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keith



Joined: 19 Sep 2005
Posts: 3136
Location: near Detroit, Michigan, USA

PostPosted: Sat Sep 16, 2006 12:22 pm    Post subject: DB Saturday Puzzle - September 16, 2006 Reply with quote

Puzzle: DB091606 ******
Code:
+-------+-------+-------+
| 6 2 . | . 7 4 | 9 . . |
| . . 7 | . . 9 | . . . |
| 3 . 4 | . . . | 2 1 . |
+-------+-------+-------+
| . . . | . 4 5 | . . . |
| 9 . 3 | . . . | 5 . 4 |
| . . . | 9 1 . | . . . |
+-------+-------+-------+
| . 8 6 | . . . | 3 . 1 |
| . . . | 5 . . | 6 . . |
| . . 1 | 8 6 . | . 5 9 |
+-------+-------+-------+


Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5065
Location: Rochester, NY, USA

PostPosted: Sat Sep 16, 2006 4:57 pm    Post subject: Reply with quote

This puzzle allowed a fair number of cells to be solved early on. A Finned X-Wing and a breakup of a deadly pattern were of little help and I reached a position, which I posted, at which the only solution for me was a chain. However, while studying my post I noticed I had missed a couple of locked candidates--excuse me, box-line interactions Very Happy --so I deleted my post and eliminated some more candidates. Now an XY-Wing was exposed, that solved a cell and everything opened up.
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keith



Joined: 19 Sep 2005
Posts: 3136
Location: near Detroit, Michigan, USA

PostPosted: Sat Sep 16, 2006 5:53 pm    Post subject: Another solution Reply with quote

I got it to here:

Code:
+----------------+----------------+----------------+
| 6    2    8    | 1    7    4    | 9    3    5    |
| 1    5    7    | 23b  23B  9    | 48   468  68   |
| 3    9    4    | 6    5    8    | 2    1    7    |
+----------------+----------------+----------------+
| 78   67   2    | 37   4    5    | 1    9    368  |
| 9    1    3    | 27B  8    26   | 5    267# 4    |
| 478  467  5    | 9    1    236  | 78   2678 2368 |
+----------------+----------------+----------------+
| 5    8    6    | 4    9    27a  | 3    27A  1    |
| 247  347  9    | 5    23b  1    | 6    2478 28   |
| 247  347  1    | 8    6    237  | 47   5    9    |
+----------------+----------------+----------------+

Marty, I presume your finned X-wing is in there somewhere. If so, can you point it out?

I used strong links (multi-coloring) on <2>. There are two chains of strong links, connected by a weak link in box 8. Using the same logic as a fork, at least one of A and B must be <2>. So, R5C8 (#) cannot be <2>.

A line-box interaction then gets you to here:
Code:
+----------------+----------------+----------------+
| 6    2    8    | 1    7    4    | 9    3    5    |
| 1    5    7    | 23   23   9    | 48   468  68   |
| 3    9    4    | 6    5    8    | 2    1    7    |
+----------------+----------------+----------------+
| 78   67   2    | 37   4    5    | 1    9    368  |
| 9    1    3    | 27   8    26   | 5    67   4    |
| 478  467  5    | 9    1    36   | 78   2678 2368 |
+----------------+----------------+----------------+
| 5    8    6    | 4    9    27   | 3    27   1    |
| 247  347  9    | 5    23   1    | 6    2478 28   |
| 247  347  1    | 8    6    237  | 47   5    9    |
+----------------+----------------+----------------+

There are three XY-wings to choose from.

Two of them are in R57C68. The first (26, 67, 27) eliminates <2> in R7C6. The second (27, 26, 67) eliminates <7> in R7C8. This is a (sort of trivial) example of overlapping wings, where the candidate elimination of one wing destroys the other wing.

Keith
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TKiel



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

PostPosted: Sat Sep 16, 2006 7:13 pm    Post subject: Reply with quote

I'll attempt to answer, maybe Marty saw a different one.

X-wing in r67c68 with fin in r6c9.

Makes the same exclusion as the multi-colouring you used.
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Marty R.



Joined: 12 Feb 2006
Posts: 5065
Location: Rochester, NY, USA

PostPosted: Sat Sep 16, 2006 9:08 pm    Post subject: Reply with quote

I don't know if my finned wing was the same as Tracy's, but I do know that it was on "2."
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