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Two XY-wings in one?

 
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Dralex

Joined: 28 Mar 2006
Posts: 7
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Location: Guenselsdorf, Austria

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PostPosted: Sat Jun 24, 2006 9:37 am    Post subject: Two XY-wings in one? Reply with quote

Hello!

I had a nice extreme puzzle in SimpleSudoku. Standard methods brought me this far:

Code:

 *-----------*
 |...|.52|..3|
 |...|4.8|.2.|
 |...|.3.|8..|
 |---+---+---|
 |69.|..5|24.|
 |.2.|...|.1.|
 |.14|2..|.89|
 |---+---+---|
 |..2|.9.|...|
 |.6.|8.1|...|
 |1..|76.|...|
 *-----------*


 *-----------*
 |.81|.52|4.3|
 |...|418|.2.|
 |24.|.37|8.1|
 |---+---+---|
 |693|185|247|
 |827|349|.1.|
 |514|276|389|
 |---+---+---|
 |472|593|168|
 |.6.|821|..4|
 |1.8|764|..2|
 *-----------*

 
 *-----------------------------------------------------------*
 | 79    8     1     | 69    5     2     | 4     79    3     |
 | 379   35    569   | 4     1     8     | 5679  2     56    |
 | 2     4     569   | 69    3     7     | 8     59    1     |
 |-------------------+-------------------+-------------------|
 | 6     9     3     | 1     8     5     | 2     4     7     |
 | 8     2     7     | 3     4     9     | 56    1     56    |
 | 5     1     4     | 2     7     6     | 3     8     9     |
 |-------------------+-------------------+-------------------|
 | 4     7     2     | 5     9     3     | 1     6     8     |
 | 39    6     59    | 8     2     1     | 579   3579  4     |
 | 1     35    8     | 7     6     4     | 59    39    2     |
 *-----------------------------------------------------------*

Now I see two XY-wings with R9C2 being the stem in both: one is
R8C1/R9C2/R9C7 and the other one is
R8C3/R9C2/R9C8.
These two XY-wings cannot both be true. How can I find out which is the right one?

Dralex[/code]
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rkral

Joined: 21 Oct 2005
Posts: 233
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PostPosted: Sat Jun 24, 2006 10:29 am    Post subject: Re: Two XY-wings in one? Reply with quote

Dralex wrote:
one is
R8C1/R9C2/R9C7 and the other one is
R8C3/R9C2/R9C8.
These two XY-wings cannot both be true.

Both XY-wings make the same exclusions, so there's no conflict that I can see.
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Carcul

Joined: 29 Dec 2005
Posts: 50
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Location: Coimbra, Portugal

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PostPosted: Sat Jun 24, 2006 12:01 pm    Post subject: Reply with quote

Dralex, the hidden single in row 1 could perhaps simplify things a little.

Carcul
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Dralex

Joined: 28 Mar 2006
Posts: 7
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Location: Guenselsdorf, Austria

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PostPosted: Sat Jun 24, 2006 8:04 pm    Post subject: Reply with quote

Hi Carcul,

Thank you. It did, when I took a hint which of course gave me that hidden single. How blind can a man get?

Dralex
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