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Tough Sudoku for 17/September/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: Gath

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Lovely calm water. I wouldn't mind being on a cruise ship if it stayed as calm as that.
I love Coast Guard men!!!
Good morning to all! Nice picture, but where is the water skier?
Good mAen. Great to see the Coast Guard in action. 9:32
Took me ages and I used pencil and paper to help me, but I got it without any guessing! Finding new strategies all the time!

Only went on a big boat once and I got terribly sea sick which surprised me since I love going on amusement park rides.
I love the water! Is this the Caribbean? Alaska?
etc? I wish I were there now.
1) Start 22, Unique Possibilities to (UP) 27.
2) Hidden pair 45 at ab2 forbids a2=6, b2=268, b1=5, c1=5, a3=4. UP 34.
3) h9=1 == h1=1 -- h1=6 == h8=6 -- h8=7 == g7=7 forbids g7=1. UP 35.
4) h8=7 == b8=7 -- a7=7 == a4=7 forbids h4=7.
5) f5=5 == f5=6 -- f2=6 == f2=1 -- f6=1 == e6=1 More...
Greg - swimming cat got him?

Thank the Lord for this day.
What a way to go!!! Great pic.
A very poor proof:
Possible proof of tough sudoku of 09 17 06:

1) Start at 22 filled - the given puzzle. Unique Possibilities to 27 filled. (UP 27).
2) Hidden pair 45 at ab2 forbids a2=6, b2=268, a3=4, bc1=5 UP 34
3a) Locked 2's at bc1 forbids ghi1=2
3b) g7=7 == h8=7 -- h8=6 More...
Perhaps if someone wishes to combine some steps, Clark's depth 6 forbidding of f6=5 combined with some of my steps, now truncated, perhaps one can yield a proof with fewer depth 6 steps. (No more than 2, for certain, perhaps just one depth 6 step is possible)
Of course, it is also possible that someone can present a depth 5 solution.
Our proofs are similar except that Steve found a way to forbid b8=4 while I found a way to forbid f6=5. Life is simpler if you do both, and here is an updated proof that does that:

1) Start 22, Unique Possibilities to (UP) 27.
2) Hidden pair 45 at ab2 forbids a2=6, b2=268, b1=5, c1=5, More...
make the tough ones TOUGHER !!!
17/Sep/07 11:31 PM
Nov. 23, 2007.
24/Nov/07 3:11 PM

05/Sep/10 10:01 PM
09/Jan/20 11:31 PM
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