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# Tough Sudoku for 17/September/2006

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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. dos? 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 343a) Locked 2's at bc1 forbids ghi1=23b) 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 !!! 7.23 17/Sep/07 11:31 PM Nov. 23, 2007. 24/Nov/07 3:11 PM SE=8.3 05/Sep/10 10:01 PM 16:33 09/Jan/20 11:31 PM