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Tough Sudoku for 9/March/2006

                 
                 
                 
                 
                 
                 
                 
                 
                 

Choose a number, and place it in the grid above.

  1 2 3 4 5 6 7 8 9
Check out the latest post in the Sudoku Forum

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Submitted by: Gath

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Missed the sweep
eh?
Maen to all. Beautiful rose to brighten up the day.
17.56 yes, finished a tough one! It's been a while
Thought it would be hard with no nine, but found it straightforward. I'm starting to dream in sudoku.
17:12 - had me stumped for a few minutes but then it all came together.
G'Maen to all Did this in 5:00 min but with guesses Off to work now on a beautiful Spring morning
Good Maen all. 8:30 with no guesses. Lovely flower. Expecting snow here in the fair state of Utah. Hooray
1) start at 23. Unique possiblities to 28.
2) Note: c1=9 == c1=1 -- c2=1 == c2=69 establishes c5=6 -- c36=9.
a1=9 == a1=1 -- ef1=1 == d2=1 -- d5=1 == f5=1 -- f5=6 == c5=6 forbids c36=9
Depth is either 5 or 6, pending double counting of c1=9 == c1=1?
3) UP to 35: Locked 4's forbid More...
OOOPS!
Sets 5 or 6 at step 2 (+ 5) at step 3 = 10 or 11. Sorry!
TYPOS!!
1) start at 23. Unique possiblities to 28.
2) Note: c1=9 == c1=1 -- c2=1 == c2=69 establishes c5=6 -- c36=9.
c1=9 == c1=1 -- ef1=1 == d2=1 -- d5=1 == f5=1 -- f5=6 == c5=6 forbids c36=9
Depth is either 5 or 6, pending double counting of c1=9 == c1=1?
3) UP to 35: Locked 4's More...
I am a bone head!
1) start at 23. Unique possiblities to 28.
2) Note: c1=9 == c1=1 -- c2=1 == c2=69 establishes c5=6 -- c36=9.
c1=9 == c1=1 -- ef1=1 == d2=1 -- d5=1 == f5=1 -- f5=6 == c5=6 forbids c356=9
3) UP 81
Depth 5 o6 6, sets 5 or 6.
How pretty - very pretty. A single pail pink rose on a bed of water.
Beautiful rose for a cloudy day. Hopefully it will rain here.
Sorry about first proof. Only read second one. Just one fc gets three eliminations which solve the puzzle.
12:17 - best for tough yet. Did not seem difficult, though.
alternative solution:
1) start 23. Up to 28.
2) Locked 1's forbid a12=1.
c2=1 == d2=1 -- d5=1 == f5=1 -- f5=6 == c5=6 forbids c2=6.
Pair 19 at c12 forbids 9 at c356.
3) UP to 81
depth 3, sets 6.
Very nice, Steve. Here's another appproach. I'll let you total the score.
1. Unique possibilities to 27.
2. Naked triplet 249 in Be2 => eliminations and i3=6. 28
3. fc: (d2=7)==(a2=7)--(a2=6)==(a4=6)--(c5=6)==
(f5=6)--(f5=1)==(d5=1) => d2<>1 => d2=7. Fill to 81.
One step before the fill to 81: locked 18 pairs in R1 => c1=9.
Hi DJ!
Very nice proof. BTW, you do not need the pair 18. I tried your proof and it works without it.
It looks like depth 4, sets 7. Definately better that my first proofs... About equal to the last one I submitted. I tend to get hung up on techniques I consider 'interesting' rather than do the efficient one first.
21:03 - least guesses for ages. Felt good.

Getting late now, G'meaNy to all.
I think I like your proof better, DJ. Your proof solves a cell with one step, then solves the puzzle with a fc. Versus my last proof, which solves nothing with the first two fc's before solving the puzzle with the third fc.
Thus, your proof is more natural, mine seems less so.
Both proofs are a huge improvement over doing all the 'easy' eliminations, still to get stuck at 29 filled needing an fc. At least, that is the way I see it.
10'45, one very lucky guess. G'Maen, all.
I agree, Steve. My first time through, I did a lot of locked-set eliminations which didn't help at all in the final analysis. But I missed your fc.
Could someone direct me to a loction where I can translate some of the posted proofs (like Steve's of DJ's). I simply need a translation of, for example, 'd2=7==a2=7--a2=6==a2=4--...'. Is this saying 'if d2 is 7 then a2 isn't 7 and thus a2 is 6 and so a2 isn't 4' and so on?
That should say '...like Steve's OR DJ's...'.
(I hate typos!)
Hi Sean - click on 'proofs' at the bottom of the page. GB has a website where the terminology is explained.
Well, we can all give up now. Scientists have developed a biological imaging algorithm that solves ALL Sudoku puzzles. Here is the article...
http://www.news.cornell.edu/ stories/Feb06/Elser.sudoku.lg.html
Of course it wouldn't be so much fun then!
Great puzzle today, managed to finish it before breakfast. After 36 filled forbid 9 at h5, then forbid 7 at f1.
20:21 Hi to all
Because it is raining today, and I have little else that needs to be done, I muse which of the following identical 5 sets, depth 5 solutions is easier to read. Both at 28 filled after Unique Placements only.
A) c2=69 == c2=1--c1=1 ==c1=9 == c1=1 -- ef1=1 == d2=1 -- d5=1 == f5=1 -- f5=6 == More...
Pretty easy actually - nice Rose
5.33, with no guesses.
I've read the links and pages on proofs, but don't recall seeing Nishio. Can someone enlighten, please? Thanks!
20.24 with one huess...think i'm getting better but its difficult
15:27 with a guess! Good mAen all!
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