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June 6 DB

 
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Earl



Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
PostPosted: Sat Jun 06, 2009 2:19 pm    Post subject: June 6 DB Reply with quote
The June 6 DB was a two-stepper for me. (Norm will find a single shot.)

Solution: x-wing (6) opens an xy-wing (138)

Earl

Code:

+-------+-------+-------+
| 2 . . | 3 . 6 | . . 1 |
| . . . | . 2 . | 4 9 6 |
| . . 5 | . . . | . . . |
+-------+-------+-------+
| 8 . . | . . 3 | . 2 . |
| . 4 . | . . . | . 3 . |
| . 5 . | 2 . . | . . 7 |
+-------+-------+-------+
| . . . | . . . | 9 . . |
| 3 9 4 | . 1 . | . . . |
| 6 . . | 9 . 7 | . . 5 |
+-------+-------+-------+

Play this puzzle online at the Daily Sudoku site
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Louise56



Joined: 21 Sep 2005
Posts: 94
Location: El Cajon, California USA
PostPosted: Sat Jun 06, 2009 2:44 pm    Post subject: Reply with quote
I solved it the same way that Earl did. I must be getting better at these. I could not solve last weeks puzzle. I tried it 3 times and could not do it.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741
PostPosted: Mon Jun 08, 2009 5:07 am    Post subject: Reply with quote
this isn't the easiest one step, but its always interesting to find.

Code:
.---------------.---------------.---------------.
| 2    8    9   | 3    4    6   | 7    5    1   |
| 1    3    7   | 58   2    58  | 4    9    6   |
| 4    6    5   | 1    7    9   | 23   8    23  |
:---------------+---------------+---------------:
| 8    1    6   | 7    9    3   | 5    2    4   |
| 7    4    2   | 68   5    1   | 68   3    9   |
| 9    5    3   | 2    68   4   | 168  16   7   |
:---------------+---------------+---------------:
| 5    7   *18  | 4    368 *28  | 9    16  *238 |
| 3    9    4   | 568  1    258 | 26   7    28  |
| 6    2   *18  | 9   *38   7   |*1-3  4    5   |
'---------------'---------------'---------------'


focusing on the marked cells in the bottom third of the puzzle.
Code:
+--------+---------+----------+
| . . 18 | . .  28 | .  . 238 |
| . . .  | . .  .  | .  . .   |
| . . 18 | . 38 .  | 13 . .   |
+--------+---------+----------+

notice how there can be a xy-wing made if the 8 in r7c9 is false.
looks like this: (imagine this in your head)
Code:
+--------+---------+---------+
| . . 18 | . . *28 | .  .*23 |
| . . .  | . .  .  | .  . .  |
| . . 18 | .*38 .  | 13 . .  |
+--------+---------+---------+

see the xy-wing? it eliminates the 3 in r9c7, keep this in mind.

now lets say the xy-wing is false
looks like this:(imagine this in your head)
Code:
+--------+-------+--------+
| . . 18 | . . . | .  . 8 |
| . . .  | . . . | .  . . |
| . . 18 | . . . | 13 . . |
+--------+-------+--------+

r7c9 = 8, leads to r9c3 is 8, leads to r9c7=1, r9c7 is not 3.
see how the 3 can't exist in r9c7?? sound familiar?? either way the 3 doesn't exist in r9c7
bingo!

xy-wing[(38)r9c5, (28)r7c6, (23)r7c9] = (8)r7c9 - (8)r7c3 = (8-1)r9c3 = (1)r9c7; r9c7 <> 3

either the xy-wing exists means r9c7 <> 3
or the 1 exists in r9c7, means r9c7 <> 3

Last edited by storm_norm on Mon Jun 08, 2009 6:17 pm; edited 1 time in total
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA
PostPosted: Mon Jun 08, 2009 3:23 pm    Post subject: Reply with quote
Quote:
there you have a nice "almost xy-wing".
this way of using a xy-wing that is almost there is not new, there are posters in the players forum who employ it.

Norm,

This was discussed here some months ago and was given the name "Finned XY-Wing." I don't think many here have used it, or at least, there hasn't been much talk about it since. I personally try to avoid it, but have no quarrel with its use.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
PostPosted: Mon Jun 08, 2009 5:02 pm    Post subject: Reply with quote
There is a 4-cell chain (extended XY-wing) 16 13 38 68 which takes out <6> in R6C8 and solves the puzzle.

Keith
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storm_norm



Joined: 18 Oct 2007
Posts: 1741
PostPosted: Mon Jun 08, 2009 6:18 pm    Post subject: Reply with quote
Marty R. wrote:
Quote:
there you have a nice "almost xy-wing".
this way of using a xy-wing that is almost there is not new, there are posters in the players forum who employ it.

Norm,

This was discussed here some months ago and was given the name "Finned XY-Wing." I don't think many here have used it, or at least, there hasn't been much talk about it since. I personally try to avoid it, but have no quarrel with its use.


Idea
thanks Marty,
I was wondering if this wasn't discussed here or not. I do remember the discussions on the finned xy-wing but didn't follow it as closely as I should have.
I took out the mentions of it being a almost xy-wing.
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