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Feb 5 VH

 
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Clement



Joined: 24 Apr 2006
Posts: 1110
Location: Dar es Salaam Tanzania

PostPosted: Sat Feb 04, 2012 11:39 pm    Post subject: Feb 5 VH Reply with quote

After the Basics
Code:
[code]
+-----------+---------+------------+
| 6  5  1   | 9 4  7  | 8   2   3  |
| 8  7  2   | 1 6  3  | 4   9   5  |
| 4  3  9   | 2 8  5  | 16  17  67 |
+-----------+---------+------------+
| 59 28 358 | 7 19 6  | 15  34  24 |
| 1  6  4   | 3 5  2  | 7   8   9  |
| 7  29 35  | 4 19 8  | 156 13  26 |
+-----------+---------+------------+
| 59 1  6   | 8 3  49 | 2   457 47 |
| 3  4  7   | 5 2  1  | 9   6   8  |
| 2  89 58  | 6 7  49 | 3   45  1  |
+-----------+---------+------------+
[/code]BUG+2
Either r6c7=1 or r7c8=4
By the following chains
If r6c7=1 =>r6c8=3 =>r4c8=4 =>r9c8=5
If r7c8=4 =>r9c8=5. We deduce that r9c8=5 which solves it.
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hughwill



Joined: 05 Apr 2010
Posts: 422
Location: Birmingham UK

PostPosted: Sun Feb 05, 2012 10:31 am    Post subject: Reply with quote

Code:

+----------+---------+------------+
| 6  5  1  | 9 4  7  | 8   2   3  |
| 8  7  2  | 1 6  3  | 4   9   5  |
| 4  3  9  | 2 8  5  | 16  17  67 |
+----------+---------+------------+
| 59 28 38 | 7 19 6  | 15  34  24 |
| 1  6  4  | 3 5  2  | 7   8   9  |
| 7  29 35 | 4 19 8  | 156 13  26 |
+----------+---------+------------+
| 59 1  6  | 8 3  49 | 2   457 47 |
| 3  4  7  | 5 2  1  | 9   6   8  |
| 2  89 58 | 6 7  49 | 3   45  1  |
+----------+---------+------------+

Play this puzzle online at the Daily Sudoku site

There's a naked triple 159 on r4 to come out in basics. (see grid)
A 135 XY centred on r6c8
also sorts out the puzzle (select text to reveal)
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kuskey



Joined: 10 Dec 2008
Posts: 141
Location: Pembroke, NH

PostPosted: Sun Feb 05, 2012 4:59 pm    Post subject: Feb 5 VH Reply with quote

The solution that leaps off the grid is the 135 xy-wing with pivot at r6c8 setting r4c1 and r6c7<>5.

Clement, your basic work is not quite complete--after taking the 159 triple in r4, r4c3<>5. Now if you assume r7c8=4, you force a conflict in 4s at r4c8. IMHO, the correct solution for the BUG+2 is r6c7=1.
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Marty R.



Joined: 12 Feb 2006
Posts: 5770
Location: Rochester, NY, USA

PostPosted: Sun Feb 05, 2012 5:13 pm    Post subject: Reply with quote

Quote:
Clement, your basic work is not quite complete--after taking the 159 triple in r4, r4c3<>5. Now if you assume r7c8=4, you force a conflict in 4s at r4c8. IMHO, the correct solution for the BUG+2 is r6c7=1.

I don't know that there's such a thing as a "correct" solution for a BUG+2. Any valid technique that works is correct.

For example, on all BUGs+2 I get greater enjoyment from using pincers. We have the two possibilities of 1 and 4. The 1 proves a 4 in r4c8, which with the 4 in r7c8 sets r9c8<>4.

Or the 4 proves 1 in r6c8, which with the 1 in r6c7 sets r6c5<>1.

There are additional possibilities with pincers as well, such as the 4 proving a 1 in r4c5.

Neither these nor Clement's solution are "incorrect."
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Clement



Joined: 24 Apr 2006
Posts: 1110
Location: Dar es Salaam Tanzania

PostPosted: Mon Feb 06, 2012 8:52 am    Post subject: Feb 5 VH Reply with quote

kuskey, it depends on which path you take. For example in this puzzle there are 8 cells which come out with the the same solution whether r6c7=1 or r7c8=4. These are the true solutions to those cells, e.g r4c1=9 whatever the choice of the solution in r6c7 and r7c8 as explained above, but, it is a long path. I decided to take a short path.
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