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Set H Puzzle 17
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Marty R.



Joined: 12 Feb 2006
Posts: 5160
Location: Rochester, NY, USA

PostPosted: Wed Dec 24, 2008 4:53 pm    Post subject: Reply with quote

I wrote:

Quote:
In boxes 47, the 12 UR is both a Type 2 and Type 4. As a Type 4, the 6 is a strong link in c3 and after removing the 1s, just one 1 remains in c3.


I apologize to all who took the time and effort to respond to the above idiocy. I've executed hundreds of Type 4 URs--and have probably explained them to new players--but I just went brain-dead, probably due to creeping (galloping?) senility, by talking about the 6s as if they were one of the deadly candidates. Embarassed Embarassed Embarassed Embarassed
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keith



Joined: 19 Sep 2005
Posts: 3174
Location: near Detroit, Michigan, USA

PostPosted: Wed Dec 24, 2008 6:27 pm    Post subject: Reply with quote

Quote:
keith: Do you have an example of a UR Type 4 w/o this X-Wing pattern?

No, I do not.

Code:
 +------------------------------------+
 |  /  123 /  |  /  /  124|  /  /  18 | < no 2 in /
 |  .  167 .  |  15 .  .  |  .  .  .  |
 |  .  12  .  |  .  .  12 |  .  .  .  |
 |------------+-----------+-----------|
 |  .  .   .  |  .  .  .  |  .  .  .  |
 |  .  .   .  |  .  .  .  |  .  .  .  |
 |  .  .   .  |  .  .  .  |  .  .  .  |
 |------------+-----------+-----------|
 |  .  .   .  |  .  .  .  |  .  .  .  |
 |  .  .   .  |  .  .  .  |  .  .  .  |
 |  .  .   .  |  .  .  .  |  .  .  .  |
 +------------------------------------+
Every Type 4 UR is also an X-wing.

But, the logic for the example above is: One of the deadly candidates <12> cannot be in the UR cells in R1. If there are no other candidates <2> in R1, <2> must stay and <1> can be eliminated.

Of course, the X-wing is there, but we are really not using it.

To continue the controversy: The Type 4 UR eliminates the DP candidate that is NOT the X-wing candidate. So, what is the reason to do X-wings before UR's? I do not see how a UR can destroy an X-wing elimination.

Keith Razz
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Wed Dec 24, 2008 7:15 pm    Post subject: Reply with quote

keith wrote:
Code:
 +------------------------------------+
 |  /  123 /  |  /  /  124|  /  /  18 | < no 2 in /
 |  .  167 .  |  15 .  .  |  .  .  .  |
 |  .  12  .  |  .  .  12 |  .  .  .  |
 |------------+-----------+-----------|
 |  .  .   .  |  .  .  .  |  .  .  .  |
 |  .  .   .  |  .  .  .  |  .  .  .  |
 |  .  .   .  |  .  .  .  |  .  .  .  |
 |------------+-----------+-----------|
 |  .  .   .  |  .  .  .  |  .  .  .  |
 |  .  .   .  |  .  .  .  |  .  .  .  |
 |  .  .   .  |  .  .  .  |  .  .  .  |
 +------------------------------------+
Every Type 4 UR is also an X-wing.

But, the logic for the example above is: One of the deadly candidates <12> cannot be in the UR cells in R1. If there are no other candidates <2> in R1, <2> must stay and <1> can be eliminated.

Of course, the X-wing is there, but we are really not using it.

To continue the controversy: The Type 4 UR eliminates the DP candidate that is NOT the X-wing candidate. So, what is the reason to do X-wings before UR's? I do not see how a UR can destroy an X-wing elimination.

Okay!!! I think we are finally on the same page. Smile

I use Simple Sudoku to highlight candidates (and pairs) when I'm manually looking for patterns. (I'd die if I had to use P&P!) The second I spot an X-Wing pattern for a candidate, I stop to see if there's a UR Type 4 present. On rare occasions, I'll remember to check for a UR Type 6. So, I use the X-Wing pattern.

Yes. Neither the X-Wing nor the UR would influence each other. But finding an X-Wing might lead one to stop and immediately check for a UR Type 4/6 in the cells from the X-Wing.

Thanks for a great exchange, Danny
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