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Tough Sudoku for 6/February/2006


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

  1 2 3 4 5 6 7 8 9
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Submitted by: sudoku lover

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It's a new day.Good MAEN all
Hints for today (proof may be simplified later):
1) easy fillings to 27.
2) basic eliminations (11 sets), then easy fillings to 37.
3) looking at 1 in col a, eliminate a9=5 (3 sets).
4) eliminate g3=5 (makes pbm with 4s in row 6, 4 sets), then easy fillings to the end.

Total cost 18 sets to look at, max depth : 4 (in step 4).
Hi Gath,
A new window appears right of this page, remembering some basic tips.
May I insist that first two tips : 'sole' and 'unique candidate' should be given in a single tip ? Understanding that the set of possible values in a cell plays exactly the same role than the set of possible More...
let's go seahawks!
That was good one.hope you all had a good weekend.
15:02 how lovely, a pyramid
Pretty easy (for a change for me) for a tough. Still do not want to time myself though.
7:23 No problems with todays puzzles.
Hanging head in shame. That was like climbing to the top of a pyramid - I thought I'd never get there. I will try again later after a cup of tea.
Go Seahawks!
On what basis did you eliminate a9=5??
Also did not see the 4 sets of 4s in step 4.
Maybe I need more coffee this early morn, but would appreciate it if you could point me towards an explanation. Easy fillings to 37, yes, wish I knew why your hints worked so easily.
12:11. Way too easy. I might have to work on som archives or study some to help on the really tough ones. that x-wing thing I finally understand, but I'm not every left with the ability to do it. Oh well.

Gath, I like seeing the previous pictures at the bottom
21:15 - but used 'check moves' several times. Still, pretty good for me! Good Maen all.
I'm taking the puzzle with me today, Sunday here will fill in as my day progresses. Good mean to all.
OH! Good MAEN everyone. LOL on the seahawks one. Go Steelers. Great picture. I'm definitely getting better at this. 5 and a few today. Thank you.
Yes same as Cleo. Easy to 37, but I don't see elimination of a9=5.
11:37 today, a great time for me on the tough puzzle
Mary and Cleo,
An explanation: if a6=1, a9=9 (col), and therefore not 5
if a8=1, c7 is not 1 (bl), e7=1 (row), e9=5 (col) and a9 is not 5
Hi Cleo,
I said 'look at 1s in col a : whether a8=1 (giving c7=5%cell) or a6=1 (giving a9=9%col) we can't have a9=5.

For the g3=5 elim, the four needed sets are :
a23=5:5s in col a
a26=4:4s in col a
e46=4:4s in col e
g4=45:values in g4.

Now forget the grid and look More...
Cleo : of course, if you can read fcs, it's just:

(a9=9)==(a6=9)--(a6=1)==(a8=1)- -(c7=1)==(c7=5) forbids a9=5


(a3=5)==(a2=5)--(a2=4)==(a6=4)--(e6= 4)==(e4=4)--(g4=4)==(g4=5) forbids g3=5.
Christina and gb,
Thank you both for the help. I still need to look at it later, because I am just not getting it today!
Good Maen!
did it!!!
Where can I learn how to read fc's?
Clyde the Newfie died in a fire and was burnt pretty badly and the morgue needed someone to identify the body. So they sent for his two best friends, Danny and Joey. Danny went in and the mortician pulled back the sheet.
Danny said,'Yes bye, he's burnt pretty bad. Roll him over.'
So the More...
and said: 'No, it ain't Clyde.'
The mortician asked, 'How can you tell?'
Joey said: 'Well, Clyde had two a*sholes.'
'What? He had two assholes?' said the mortician.
'Yes bye, everyone in town knew he had two assholes. Every time the three of us went to town, folks would say:
'Here comes Clyde with them two a*sholes.'
mary : just google 'forbidding chains' or follow 'proofs' link bottom page here, then 'Bruno's proofs'.
3:22 after setup - was it easy or am I just kidding myself? I think it's definitely the second possibility... Good MAEN to all, but especially to all the STEELERS fans out there today! One for the thumb!!!
Thanks! I've always followed chains but using sets is much faster...I think...once you see them! My problem with row 6 and g were I forgot the simple eliminations. It was staring me in the face and I just couldn't see it.
6:03 start to finish.
And yes I am improving.
Only been doing su-doku for a month and LOVING it!

Good MAEN to all!
OK here is what I did: It looks very similar, upon just a cursory glance, to gb.
Easy fillings to 27: pair 12 box h2 exclude 2 at h3: Easy fillings to 37. One need do none of the other available eliminations.
(a2=4)==(a6=4)--(e 6=4)==(e4=4)--(g4=4)==(g4=5)--(g3=5)==(i 2=5) forbids More...
Now reading gb's fcs, I see that I am not too bright! My second fc could lose a (weak/strong) pair! My first fc is ok, - it just sees a slightly different contradiction in the 4's. Again, I am amazed that these proofs seem to zero in on many of the same sets and ideas! As per usual, gbs proofs are much better though.
So it seems today's puzzle requires at most 3 eliminations: the way I did it was: h3<>2 by pair 12, a2<>5 by fc, a9<>5 by fc.
What a great picture of an ... awesome pyramid!

I finished this 'tough' puzzles in 57 minutes and fourteen seconds...a piece of cake!

Is there a harder puzzle than Tough?

If so, bring it on!

I screwed up placing my possibilities in and had to redo the puzzle... twice! It seemed pretty easy; then again, maybe I need to redo it later again today to see if I was still placing numbers where they should/shouldn't have been. Good maen, all. I see Gath has been playing with fonts and pics :)
I love the native art for the Seahawks' logo, and bought a shirt with it. I don't actually follow football, just baseball, but it is such a beautiful design, I couldn't resist. Hope it is a great game, for those who will watch it.

7:24 total time, 3:55 setup, 2:29 solving.
Bow to GB. Yet another epiphany regarding fc's. In addition to pincering, they can 'strangle', as in the a9<>5 elimination. A caution on sets to Cleo and Mary: there must be, if not a strong, at least a weak coupling leading from one set to another. PS to Sarah: your jokes are funny, but let's keep the language at the same high tone level of civility as the rest of the conversation.
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