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1/17 VH

 
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Thu Jan 17, 2008 12:51 am    Post subject: 1/17 VH Reply with quote

Code:
4       7       1       | 2       5       8       | 3       9       6
2       9       58      | 167     16      3       | 157     18      4
6       3       58      | 17      9       4       | 157     2       78
---------------------------------------------------------------------
8       5       7       | 69      3       269     | 26      4       1
3       6       2       | 4       17      17      | 8       5       9
9       1       4       | 5       8       26      | 267     3       27
---------------------------------------------------------------------
1       2       6       | 8       4       5       | 9       7       3
5       4       9       | 3       67      67      | 12      18      28
7       8       3       | 19      2       19      | 4       6       5


after basics
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cgordon



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

PostPosted: Thu Jan 17, 2008 2:50 pm    Post subject: Reply with quote

Quote:
after basics

Yeah but what about after non-basics!! I'm stuck.

I did find an X-wing that got rid of <7> in R2C5 but that didn't seem to do anything.

I'm not into chains - is there another way??
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Johan



Joined: 25 Jun 2007
Posts: 206
Location: Bornem Belgium

PostPosted: Thu Jan 17, 2008 3:33 pm    Post subject: Reply with quote

Quote:
I'm not into chains - is there another way??


cg, look for an xy-wing
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sdq_pete



Joined: 30 Apr 2007
Posts: 119
Location: Rotterdam, NL

PostPosted: Thu Jan 17, 2008 3:44 pm    Post subject: Reply with quote

The X-wing on 7's leaves a triplet in C5 followed by "XY 178 R3C9".

Peter
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Marty R.



Joined: 12 Feb 2006
Posts: 5732
Location: Rochester, NY, USA

PostPosted: Thu Jan 17, 2008 6:04 pm    Post subject: Reply with quote

This puzzle offered an excellent opportunity for a technique I learned just recently and which I had used just once before now, namely, Aligned Pair Exclusion (APE).

Code:

+--------+------------+-----------+
| 4 7 1  | 2   5  8   | 3   9  6  |
| 2 9 58 | 167 16 3   | 157 18 4  |
| 6 3 58 | 17  9  4   | 157 2  78 |
+--------+------------+-----------+
| 8 5 7  | 69  3  269 | 26  4  1  |
| 3 6 2  | 4   17 17  | 8   5  9  |
| 9 1 4  | 5   8  26  | 267 3  27 |
+--------+------------+-----------+
| 1 2 6  | 8   4  5   | 9   7  3  |
| 5 4 9  | 3   67 67  | 12  18 28 |
| 7 8 3  | 19  2  19  | 4   6  5  |
+--------+------------+-----------+

Play this puzzle online at the Daily Sudoku site

In r3c79 the six possible combinations are 17-18-57-58-77-78. 77 is impossible and 18-58-17 are eliminated because of the bivalue cells in box 3 and row 3. Thus the remaining possibilities for r3c79 are 57-58. A 1 is no longer a possibility for r3c7 and the puzzle is solved.

Of course, the XY-Wing accomplishes the same thing, but the APE was much more fun.
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cgordon



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

PostPosted: Thu Jan 17, 2008 6:41 pm    Post subject: Reply with quote

That Ape thing is cool. Sure beats looking for xy-wings. I'd have difficulty spotting the xy-wing if there were only 3 unsolved cells left. I used the Forum Offered method this morning. So let's Go Ape eh - A pox on wings.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Thu Jan 17, 2008 8:58 pm    Post subject: Reply with quote

put me down for the xy-wing {1,7,8} r2c8, r3c9, r3c4

takes out the 1's in r2c45
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tlanglet



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

PostPosted: Thu Jan 17, 2008 11:16 pm    Post subject: Reply with quote

Marty R. wrote:
This puzzle offered an excellent opportunity for a technique I learned just recently and which I had used just once before now, namely, Aligned Pair Exclusion (APE).


Marty,

I have read about APE and reviewed the included examples, but I have never understood the clues or hints to make it worth the time involved to examine various possibilities. What do you look for overall that suggests the strong possibility of an APE?

Ted
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eddieg



Joined: 12 Jan 2006
Posts: 47
Location: San Diego, CA USA

PostPosted: Fri Jan 18, 2008 12:38 am    Post subject: storm_norm Reply with quote

I enjoyed today's puzzle. I was stuck too until I found the same chain you found. My problem, is once I find these types of moves, and make the first elimination, I forget to see if there is a second or third elimination based on the same move.
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Marty R.



Joined: 12 Feb 2006
Posts: 5732
Location: Rochester, NY, USA

PostPosted: Fri Jan 18, 2008 1:32 am    Post subject: Reply with quote

tlanglet wrote:
Marty R. wrote:
This puzzle offered an excellent opportunity for a technique I learned just recently and which I had used just once before now, namely, Aligned Pair Exclusion (APE).


Marty,

I have read about APE and reviewed the included examples, but I have never understood the clues or hints to make it worth the time involved to examine various possibilities. What do you look for overall that suggests the strong possibility of an APE?

Ted

Ted,

I hardly qualify as an expert here, but I look for a trivalue and bivalue cell next to each other, with at least one common number. Then, between the box and the row, I want at least two bivalue cells which can cause exclusions. The situation hasn't come up often but, fortunately, it takes very little time to scan for them.
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cgordon



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

PostPosted: Fri Jan 18, 2008 2:00 am    Post subject: Reply with quote

That APE method reminds me a bit of the Sue de Coq method - which I actually learned a year ago - but have never since found an opportunity to apply. Sue de Coq is about finding two cells in a box with 5 numbers that see two pairs with 4 of those numbers. Thus - by relatively easy logic - the 5th or "unpaired" number is included in one of the cells.

Just thought I'd mention that.

(edited)
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Fri Jan 18, 2008 10:46 pm    Post subject: Reply with quote

Craig,

Your description doesn't match my understanding of Sue de Coq, but does seem to describe a sort of APE.

As I understand it, Sue de Coq involves N digits in N cells arranged in such a way that they form various locked sets amongst various houses. This produces eliminations in cells outside of those N cells. It is similar to, say, a naked triple in a single house in that regard. (I.e. three digits in three cells that eliminate those digits from other cells in that house.) And, it is not limited to 5 digits. I've seen Sue de Coq situations involving 7 or 8 digits.

I find that Sue de Coq situations are difficult to spot and so have only rarely used the technique myself.

The two methods are closely related in that they both employ locked set logic.
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cgordon



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

PostPosted: Fri Jan 18, 2008 11:31 pm    Post subject: Reply with quote

Hi Asellus: I gotta have pictures. I don't think I described the Sue de Coq correctly - but my graphic understanding is shown below.

The three cells in Box1 C2 must contain three nos.of 12389 - but can't contain a 1 AND 9 or a 2 AND 3 - otherwise the linked pairs 19 and 23 disappear. So the three cells must contain an 8. So we can remove any linked 8 from Box 1 or C2.

Hope I got that right. Anyway I have looked for months for a chance to apply this method - but as you say they are very rare. Pity, I could have looked like an expert.

Code:
            
++---------+------   
| . 389 .  | . . .   
| .12389.  | . . .   
| . 239. 23| .    
+----------+------
| .  . .   | . . . |   
| .  . .   | . . . |   
| .  . .   | . . . |   
+----------+-------+-------+   
| . . .    | .  . .| . . . |   
| . . .    | .  . .| . . . |   
| . 19 .   | .  . .| . . . |
+-------+--------+---------+
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Sat Jan 19, 2008 7:18 am    Post subject: Reply with quote

Craig,

Yes, it was your description that wasn't doing the thing justice. What you have illustrated is Sue de Coq. There are 5 cells involved: r1239c2 and r3c3. And, these 5 cells contain exactly 5 digits: {12389}. And finally, they are arranged properly: {19} is restricted to c2 in the 5 cells; {23} is restricted to b1 in the 5 cells; and the 2 <8>s are forced to be strongly linked. And, there are more eliminations possible than you are saying (this is the potentially powerful aspect of Sue de Coq): <1> and <9> are removed from r45678c2; <2> and <3> are removed from r123c1 and r12c3; and <8>s are removed from r123c1, r12c3 and r45678c2. (In the particular example you saw perhaps only <8>s were present for removal. However, without knowing anything else about the grid, all of those eliminations are possible.)
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