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Earl
Joined: 30 May 2007
Posts: 677
Location: Victoria, KS
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 Posted: Sat May 23, 2009 2:40 pm Post subject: May23 DB |
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I could not find a single bullet for this May 23 DB, so I winged it.
A Solution: x-wing (2), xy-wing (568), w-wing (86).
Earl
| Code: |
+-------+-------+-------+
| . 4 . | . 7 5 | 9 . . |
| 8 . . | . 9 . | . . 7 |
| 7 . . | . . 3 | . 1 . |
+-------+-------+-------+
| 2 . 4 | 9 . . | 1 . . |
| . 9 . | . . . | . 7 . |
| . . 3 | . . 8 | 4 . 2 |
+-------+-------+-------+
| . 3 . | 2 . . | . . 1 |
| 4 . . | . 3 . | . . 9 |
| . . 1 | 7 5 . | . 4 . |
+-------+-------+-------+
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Play this puzzle online at the Daily Sudoku site |
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arkietech
Joined: 31 Jul 2008
Posts: 1834
Location: Northwest Arkansas USA
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| Posted: Sat May 23, 2009 3:00 pm Post subject: |
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I used two steps: | Quote: | w-xing 38 on 8
finned x-wing 8 |
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Louise56
Joined: 21 Sep 2005
Posts: 94
Location: El Cajon, California USA
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| Posted: Sat May 23, 2009 5:06 pm Post subject: |
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| I solved it in two steps. After basics I looked at the 38 pair in r9c9 and could see that if I put a 3 or an 8 in the result is a 3 in r4c8. I believe this is a skyscrapper but please let me know if I am mistaken. Then I looked at the 58 pair in r4c9 and could see that if I put in a 5 or an 8 then the 8 must be removed from r5c7. Not sure what this is called. I did see a 568 wing but it wasn't helpful. |
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keith
Joined: 19 Sep 2005
Posts: 3355
Location: near Detroit, Michigan, USA
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| Posted: Sat May 23, 2009 6:00 pm Post subject: |
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After basics: | Code: | +-------------+-------------+-------------+
| 3 4 26b | 1 7 5 | 9 268 68a |
| 8 1 56 | 4 9 2 | 356 356 7 |
| 7 25c 9 | 6 8 3 | 25 1 4 |
+-------------+-------------+-------------+
| 2 58d 4 | 9 6 7 | 1 38 35-8e|
| 1 9 58 | 3 2 4 | 68 7 568 |
| 6 7 3 | 5 1 8 | 4 9 2 |
+-------------+-------------+-------------+
| 5 3 78 | 2 4 9 | 678 68 1 |
| 4 6 27 | 8 3 1 | 257 25 9 |
| 9 2-8g 1 | 7 5 6 | 238 4 38f |
+-------------+-------------+-------------+ |
Ignoring an X-wing and an XY-wing:
abcd is an extended XY-wing that takes out <8> in e.
def is then an XY-wing that takes out <8> in g, solving the puzzle.
Keith |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Sat May 23, 2009 7:58 pm Post subject: |
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| Louise56 wrote: | | I solved it in two steps. After basics I looked at the 38 pair in r9c9 and could see that if I put a 3 or an 8 in the result is a 3 in r4c8. I believe this is a skyscrapper but please let me know if I am mistaken. Then I looked at the 58 pair in r4c9 and could see that if I put in a 5 or an 8 then the 8 must be removed from r5c7. Not sure what this is called. I did see a 568 wing but it wasn't helpful. |
Louise56,
You seem to have a good grasp on taking a bi-value cell and finding an identical outcome in another cell when either of the values in your starting cell is true. I believe many would call this a dual implication chain.
As to your first move, I can't see that any skyscraper would result in the placement of 3 in r4c8. therefore, no, its not a skyscraper.
your second move, ironically, can be expressed as a skyscraper. but again, the way you describe it by assuming each value in the bi-value cell is true which in turn leads to the eimination of 8 in r5c7... I think we can safely say that you are finding dual implication chains.
if you do a google on this term, you will find lots of info on them.
-----
that said, I am going to examine your moves and give you the names that they most resemble and that have a great deal of meaning in this particular forum. 
your move #1... either the 3 or the 8 being true in A results in 3 being true in C.
in the grid is marked the cells which show your implications.
if A is 3 then B is not 3, then C is 3
If A is 8, then D is not 8, E is 8, then C is not 8, C is 3
| Code: | .---------------.---------------.---------------.
| 3 4 26 | 1 7 5 | 9 E268 D68 |
| 8 1 56 | 4 9 2 | 356 356 7 |
| 7 25 9 | 6 8 3 | 25 1 4 |
:---------------+---------------+---------------:
| 2 58 4 | 9 6 7 | 1 C38 B358 |
| 1 9 58 | 3 2 4 | 68 7 568 |
| 6 7 3 | 5 1 8 | 4 9 2 |
:---------------+---------------+---------------:
| 5 3 78 | 2 4 9 | 678 68 1 |
| 4 6 27 | 8 3 1 | 257 25 9 |
| 9 28 1 | 7 5 6 | 238 4 A38 |
'---------------'---------------'---------------' |
This is more commonly known as a W-wing.
cells ADEC in that order, or CEDA makes up the wing.
notice how the conjugate 8's in row 1 in E and D each can see a {3,8} cell, one at A(your starting cell) and the {3,8} cell at C.
because the 8's are conjugate one has to be true. this forces either of the 3's at A and C to be true thus eliminating the 3 At B and places 3 at C ( like your chain does ).
second move...either 5 or 8 in A forces 8 to be eliminated from E
A is 8, E is not 8, simple enough
A is 5, B is not 5, B is 8, C is not 8, D is 8, E is not 8
| Code: | .---------------.---------------.---------------.
| 3 4 26 | 1 7 5 | 9 268 68 |
| 8 1 56 | 4 9 2 | 3 56 7 |
| 7 25 9 | 6 8 3 | 25 1 4 |
:---------------+---------------+---------------:
| 2 B58 4 | 9 6 7 | 1 3 A58 |
| 1 9 58 | 3 2 4 |E68 7 568 |
| 6 7 3 | 5 1 8 | 4 9 2 |
:---------------+---------------+---------------:
| 5 3 78 | 2 4 9 | 678 68 1 |
| 4 6 27 | 8 3 1 | 257 25 9 |
| 9 C28 1 | 7 5 6 |D28 4 3 |
'---------------'---------------'---------------' |
the important thing to realize here is that the 8's in ABCD or DCBA form a Skyscraper.
there are only two 8's in row 4 at A and B
there are only two 8's in row 9 at C and D.
a Skyscraper is a x-wing with a bent side. the 8's at A and D don't line up, they do not share a column.
However, the 8's at BD do, they share column 2. when this happens, the 8's at A and D act like pincers. no matter which way around you go ABCD or DCBA, one of the 8's at A or D has to be true.
since they both can "see" the 8 at E, it can be eliminated.
which does exactly what your DIC (dual implication chain) accomplishes. |
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storm_norm
Joined: 18 Oct 2007
Posts: 1741
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| Posted: Sat May 23, 2009 9:07 pm Post subject: |
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| Code: | .---------------.---------------.---------------.
| 3 4 *26 | 1 7 5 | 9 268 *68 |
| 8 1 56 | 4 9 2 | 356 356 7 |
| 7 -25 9 | 6 8 3 | 25 1 4 |
:---------------+---------------+---------------:
| 2 58 4 | 9 6 7 | 1 38 358 |
| 1 9 *58 | 3 2 4 |*68 7 *568 |
| 6 7 3 | 5 1 8 | 4 9 2 |
:---------------+---------------+---------------:
| 5 3 *78 | 2 4 9 | 678 68 1 |
| 4 6 27 | 8 3 1 | 257 25 9 |
| 9 *28 1 | 7 5 6 | 238 4 38 |
'---------------'---------------'---------------' |
a one step chain
(2=6)r1c3 - (6)r1c9 = (6)r5c9 - (6=8)r5c7 - (8)r5c3 = (8)r7c3 - (8=2)r9c2; r3c2 <> 2 |
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tlanglet
Joined: 17 Oct 2007
Posts: 2468
Location: Northern California Foothills
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| Posted: Sat May 23, 2009 10:47 pm Post subject: |
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My two step solution was:
a Kraken x-wing on 8 in r14c89 and fin in r4c2 that deletes the 8 in r7c8,
xy-wing 386 with pivot 38 in r4c8 and pseudo-cell 36 in row2.
Ted |
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