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Tough Sudoku for 21/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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Good maen all in sudokuland
Sincerely hope everyone was safe from the cyclone
Steve from Ohio, you get a lot of points for just writing that proof yesterday, never mind finding it.
Lovely - Is it the Great Pyramid of Cheops?
Steve, Amen to Christina's comment.
Rose from Sydney,
It's not the different ways of solving a puzzle. I was convinced by GB early on in my doing this that one needs either to prove that there is a unique solution (we are told there is, but that's just heresay) or find all the different solutions, that is, the different sets of More...
Rose from Sydney,
BTW, we hope to be enjoying the delights of your fair city in a few weeks. Looking forward to it.
Thanks Gath for doing a slightly easier tough tonight! Made me feel a lot better.
yeah.after frustrating time with yesterday's puzzle i feel good finishing this one,though the pic is a repeat
19:11. That one was either easy or I'm getting better.

See you all tomorrow. Off to take care of the pups and then take a well needed nap!!!!!
A time too horrible to post; no pyramind power for me today. Best to all !
Hi gb. Thanks for the tips yesterday, I gave up though, it was sooooo tough!
To ap,
The pictures will always be the same for the same level of puzzle whenever you do it. Hard will have the same picture today or if you go into the archives and do one from three months ago. Tough, the same, and so on.
Question-I have found a different solve for a puzzle than what the site had as a solution. I felt I checked it over quite well, is this possible?
Good Maen all, and almost happy spring (in a couple of hours). Hope Cyclone Larry has moved away and does no more harm.

Total minutes 7:22, setup 3:44, and solving 3:38. This one was a little tough for me, lots of chaining happening!
8:01. not my best. but my mind is already at work, even though I'm still im pjs.
Steve: check out my comment on yeasterday's puzzle!
HI Bill - I read your comment. I do not understand how column H will not work. I can get a contradiction, but it takes at least 18 steps. Please let me know if the contradiction you came up with has fewer steps. Thanks!

Linda from Mass...if you're sure you have another solution, let Gath know...he may want to check it!
Hi Steve. In the Sandbox you refer to pb, what exactly does that mean?
Andrei - ouch....
Another very ugly solution:
1) Start at 23 filled. UP to 27.
2) A) Note ALS 436, 369, 49 at efg1. establish b1=3 -- f2=6.
B) f2=2 -- f6=2 == f6=5 -- i6=5
C) f2=2 -- f56=2 == e4=2 -- g4=2 == g4=9 -- i6=9.
D) Using B and C: f2=2 -- i6=59 == i6=2 -- i8=2.
E) Using A and D: a3=1 == b3=1 -- b3=3 == b1=3 -- f2=6 == f2=2 -- i8=2 == a8=2 forbids a8=1.
3) Up 31. Locked 7's forbid ab4=7. Locked 4's forbid h13=4. Colors 6's forbid h3=6. (h4==a4--c5==c3)
4) locked 7's forbid 7 at de9, f7.
5) b4=5 == b4=2 -- g4=2 == g3=2 -- h3=2 == h3=5 forbids h4=5, B3=5.
6) ALS: S1 = (35,356,346 at E179) S2= (25,29,49) at B4,g4,g1. Note only one of More...
7) Locked 5'S forbid 5 at abc5, bc6. Pair 76 at AC5 forbids 76 at a4, bhi5. UP 32.
8) Locked 3's at f5. Pair 25 forbids 25 at F72.
8) UP 81
11+ 4 + 1 + 3 + 6 + 6 = 31 sets, depth 11 at step 2.
PB - is probably short for 'problem'. I believe that is the vernacular gb uses.
Hi Andrei! A few days ago you asked about hidden pairs relative difficulty versus naked triples. Generally, I judge them about equivalent. Two months ago, a hidden pair was much harder. I suppose that it depends on what one chooses to look for first - and how often they look for it. Regarding that puzzle, I was careful to not call the use of the hidden pairs an 'imporvement'.
Or rather, an 'improvement', even!
Steve: from yesterday, at 29 filled, if G4=1, then H5=2. The rest of column H will have only four possibilities (3479) for the other five cells. Only 2 steps.
8:41---the easiest 'tough' I have ever completed
Also note that in today's puzzle, after establishing B3=1, then automatically B7=1 and you can fill to 36.
Arthur From Derbyshire, UK, Happy birthday for yesterday

Great Maen to all
Hang on a minute Bill, if b3 =1 then b7 cannot = 1 as well??
Also, how do you 'establish' where the 1 goes in C3?
Sorry, I meant column b.
Thanks Bill, but I think you are perhaps mistaken. AT 30 filled, after all normal eliminations, column H yesterday's puzzle. h1 thru h9:379,6,8,247,12,473,3479,149. Undoubtedly, we are not looking at the same configuration. Please advise how you eliminate 2 possibiiities from these 6 cells. Thank-you.

Today's puzzle, how do you establish b3=1. My solution does not have b3=1.
Also, on today's puzzle, even if I put in the correct value for b3=3, I only get to 34 filled without fc's. Still, though, I do not know how you establish that b3=3.
Finally, even if your solution for yesterday's puzzle is valid, it would have depth of 6 or 7, as that is how many strong sets considered. I may see many eliminations without taking a 'step', but that does not mean that the eliminations have zero depth.
3.38 after set up, not bad at all

and if I say that I believe you, I wonder how many would believe me!
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