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Feb 20 VH

 
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Clement



Joined: 24 Apr 2006
Posts: 1111
Location: Dar es Salaam Tanzania

PostPosted: Fri Feb 19, 2010 10:31 pm    Post subject: Feb 20 VH Reply with quote

W-Wing <57>-7=7-<57> with strong link 7 in row 5 eliminates the 5's in row 7 BOX 9 and r9c2 solving the puzzle.
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Marty R.



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

PostPosted: Sat Feb 20, 2010 2:16 am    Post subject: Reply with quote

I didn't notice the W-Wing, but the 57s could be used as an M-Wing, although it was a case of simple coloring on 7. Either way, that's all that was needed.

On my 2nd attempt an XY-Wing (275) plus pincer transport did it.
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arkietech



Joined: 31 Jul 2008
Posts: 1834
Location: Northwest Arkansas USA

PostPosted: Sat Feb 20, 2010 2:18 pm    Post subject: Reply with quote

Marty R. wrote:
a case of simple coloring on 7.

Or skyscraper 7.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Sat Feb 20, 2010 5:25 pm    Post subject: Reply with quote

XY-wings: 2-57, -457, 2-57.

Keith
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sat Feb 20, 2010 6:41 pm    Post subject: Reply with quote

... or ER on 7.
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Louise56



Joined: 21 Sep 2005
Posts: 94
Location: El Cajon, California USA

PostPosted: Sat Feb 20, 2010 7:09 pm    Post subject: Reply with quote

Can I remove the 45 in r7c8? Is there a unique rectangle there?
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tlanglet



Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills

PostPosted: Sat Feb 20, 2010 7:52 pm    Post subject: Reply with quote

Louise56 wrote:
Can I remove the 45 in r7c8? Is there a unique rectangle there?


Yes, the Type 1 UR45 in r17c78 deletes both the 4 and 5 in r7c8.

Also note the 6-cell DP on 45 in r167c789. To prevent the DP, r6c89=7, r7c9=7, or r7c9=2.
(7)r6c89 - (7=9)r6c3,
(7)r7c9 - (7=5)r9c9 - (5=9)r9c2 - (9)r6c2 = (9)r6c3,
(2)r7c9 - (2=7)r5c9 - (7=5)r9c9 - (5=9)r9c2 - (9)r6c2 = (9)r6c3.

Thus, all conditions to prevent the deadly pattern force r6c3=9 to complete the puzzle in one step.

Ted
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Wendy W



Joined: 04 Feb 2008
Posts: 144

PostPosted: Sat Feb 20, 2010 10:37 pm    Post subject: Reply with quote

Louise's UR jumped out at me as soon as I finished basics. After that, two xy-wings on 257 solved it.
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Ema Nymton



Joined: 17 Apr 2009
Posts: 89

PostPosted: Sun Feb 21, 2010 2:19 pm    Post subject: Reply with quote

.

2/20/2010

Code:

+----------+-------+----------+
| 6  7  8  | 3 2 9 | 5 4  1   |
| 9  4  2  | 5 1 6 | 7 3  8   |
| 1  3  5  | 7 4 8 | 2 6  9   |
+----------+-------+----------+
| 25 1  4  | 8 9 7 | 3 25 6   |
| 27*6  3  | 4 5 1 | 9 8  27A |
| 8  59 79 | 6 3 2 | 1 57 4   |
+----------+-------+----------+
| 57B8  1  | 9 6 3 | 4 27 257C|
| 4  2  6  | 1 7 5 | 8 9  3   |
| 3  59 79 | 2 8 4 | 6 1  57  |
+----------+-------+----------+


Why does the ABC combination not eliminate the 7 from r5c1?

Ema
~@:o|
.
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Ema Nymton



Joined: 17 Apr 2009
Posts: 89

PostPosted: Sun Feb 21, 2010 2:34 pm    Post subject: Reply with quote

.

Part II

Code:

+----------+-------+----------+
| 6  7  8  | 3 2 9 | 5 4  1   |
| 9  4  2  | 5 1 6 | 7 3  8   |
| 1  3  5  | 7 4 8 | 2 6  9   |
+----------+-------+----------+
| 25 1  4  | 8 9 7 | 3 25D6   |
| 27*6  3  | 4 5 1 | 9 8  27A |
| 8  59 79 | 6 3 2 | 1 57 4   |
+----------+-------+----------+
| 57B8  1  | 9 6 3 | 4 27E257C|
| 4  2  6  | 1 7 5 | 8 9  3   |
| 3  59 79 | 2 8 4 | 6 1  57F |
+----------+-------+----------+


Why does the ABC combination not eliminate the 7 from r5c1 but the DEF combination does eliminate the '5' from r7c9?

Ema
~@:o|
.
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Sun Feb 21, 2010 4:10 pm    Post subject: Reply with quote

Ema Nymton wrote:
.

2/20/2010

Code:

+----------+-------+----------+
| 6  7  8  | 3 2 9 | 5 4  1   |
| 9  4  2  | 5 1 6 | 7 3  8   |
| 1  3  5  | 7 4 8 | 2 6  9   |
+----------+-------+----------+
| 25 1  4  | 8 9 7 | 3 25 6   |
| 27*6  3  | 4 5 1 | 9 8  27A |
| 8  59 79 | 6 3 2 | 1 57 4   |
+----------+-------+----------+
| 57B8  1  | 9 6 3 | 4 27 257C|
| 4  2  6  | 1 7 5 | 8 9  3   |
| 3  59 79 | 2 8 4 | 6 1  57  |
+----------+-------+----------+
Why does the ABC combination not eliminate the 7 from r5c1?

Ema ~@Surprised|
.
C can be 2, 5, or 7.
If it is 2, A is 7. If it is 5, B is 7. If it is 7, you cannot make an elimination in R5C1 using only A, B, C.

Keith
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keith



Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA

PostPosted: Sun Feb 21, 2010 4:15 pm    Post subject: Reply with quote

Ema Nymton wrote:
.

Part II

Code:

+----------+-------+----------+
| 6  7  8  | 3 2 9 | 5 4  1   |
| 9  4  2  | 5 1 6 | 7 3  8   |
| 1  3  5  | 7 4 8 | 2 6  9   |
+----------+-------+----------+
| 25 1  4  | 8 9 7 | 3 25D6   |
| 27*6  3  | 4 5 1 | 9 8  27A |
| 8  59 79 | 6 3 2 | 1 57 4   |
+----------+-------+----------+
| 57B8  1  | 9 6 3 | 4 27E257C|
| 4  2  6  | 1 7 5 | 8 9  3   |
| 3  59 79 | 2 8 4 | 6 1  57F |
+----------+-------+----------+
Why does the ABC combination not eliminate the 7 from r5c1 but the DEF combination does eliminate the '5' from r7c9?

Ema ~@Surprised|

DEF does not eliminate 5 in R7C9.

Ema,

I suggest you get a copy of Sudoku Susser. It explains the "why" of every move.

It is easy to use, and Norm has videos that show some of the finer points.

Keith
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Marty R.



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

PostPosted: Sun Feb 21, 2010 4:55 pm    Post subject: Reply with quote

Quote:
DEF does not eliminate 5 in R7C9.

May I add the reason is that in this XY-Wing, E is the pivot and D and F the pincers. The pincer number is 5 and no cell with a 5 sees both pincers.

The 5 in r9c2 can be eliminated with a pincer transport, but we're getting ahead of ourselves with that.
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