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Submitted by: Gath

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it took me much more time and several guesses!it seems I do not master the X-wing techniques!
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7:44min. LOVE SUDOKU!!!!!!!
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Happy Birthday to you. Is that what the candles are for?
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What are the x wing?
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morning all still no andre,,8:58 for me today
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10:42thank god the timer didnt malfunction.
happen to see quite a few petrified comments on seeing my scandalizing 1.03 in yesterdays hard.well that was ACTUALLY the time that was displayed in the timer.i just posted it for the heck of it.nothing intentional.my time was may be around 8to10mts.ok folks .cheers
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36:47 first time getting the tough completed
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Candles. 1:19:47. No guessing. Worst time ever by a long shot. Yesterdays was 41+ minutes. Day before 31+ minutes. Best time about 25 minutes. Learnt a few things though on this one. Hope I remember the new logics for the next ones. Still can't understand how anyone can do these 'tough' ones under 10 minutes. It takes me about 8 minutes just put down the possibilities.
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How do I access past 'tough' Sukokus? Are these a one day only challenge?
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Graham - Go to the archieves. I do it every day to practice. Not that I'm any faster, but it goes way back to May.
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7:03 this morning. I'm curious about how people time. I turn on the timer when I start, before I look at the puzzle. I think some people 'set up' the puzzle first. So I'm never sure how I'm doing timewise in relation to others.
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I sometimes see questions or speculation in these comments about whether there are some puzzles where guessing is necessary. I was skeptical at first, but bg of france has convinced me that it is never never necessary to guess. See his many step by step solutions to these puzzles on his website.

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I never time tough, but wish I'd timed this one. It was the easiest I've ever done by far!
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11:53. Judy - I turn the timer on then start and don't turn it off until I'm completely finished. Sometimes it's fast, sometimes its 30 minutes before I get finished.

Today I totally screwed up and cheated by accident a few times, which lead me to correct answers.
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To Yvette and Howardl and others about gb:
Okey guys, you can't be confused when you write down gb (not jb or bg) since the first letter ('g') stands for GURU. Easy to remember, no? I don't know anything about the 'b'.
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Way too easy for 'tough'
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Start with 27 filled (b3=7 g4=4 i4=5 i5=7 h4=2 h7=7 h9=4)
pair 68 in Bh2
chain 59/69/56 in row 6 then easy to 46 filled
pair 19 in row 9 leads to 51 filled.
chain 179/179/19 in row 8.
whatever you choose in e1 (1 or 9) leads to h1=8
whatever you choose in f2 (7 or 1) leads to e5=3
easy to the end
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Complete solution. As usual, not checked for typos, and most likely not the most efficient way to solve:

Part 1

1. a8 & c8 must = 2 or 3, eliminate from other cells in row
2. In row-4, 2 must be in h4 or i4, eliminate from d4 & e4
3. In row-3, 3 must be in g3 or i3, eliminate from d3 & f3
4. Simple elimination: i5=7, h7=7, b3=7
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Part 2

5. Given step 1, 8 must be in a7 or c7; eliminate from d7, f7 & i7
6. In column-g, 8 must be in g5 or g6; eliminate from g2, g8 & g9
7. In row-6, 5, 6 & 9 must be in a6, b6 or c6; eliminate from other cells in row & 3x3
8. In row-2, 9 must be in g2 or i2; eliminate from d2, More...
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Part 3

11. In row-4, 2, 4 & 5 must be in g4, f4 & i4; elimiate from other cells in row
12. Simple elimination: d3=6 (has been eliminated from other cells in row), e8=6, i7=6
13. In column-b, 4 must be b8 or b9; eliminate from other cells in column & 3x3
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Part 4

14. Simple elimination: f7=4 (has been eliminated from other cells in row), e2=4, a3=4, c5=4, e6=7 (has been eliminated from other cells in column), f6=2, f3=5, g3=3, i3=2, i4=5, g4=4, h4=2, h9=4, b8=4, i9=3, g2=5, i2=9, i8=8
15. b9 & g9 must = 1 or 9; eliminate from other cells in row
16. Simple elimination: f9=8, d5=8, e5=5, e9=2, d9=5
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Part 5

17. Looking at e4 = 1 or 9; can conclude that d7 must = 1; proof: if e4=1, then d4=9 & d7=1; if e4=9, then e1=1, b1=6, b6=9, a7=9 & d7=1
18. Simple elimination: c7=8, a7=9, b9=1, g9=9, g8=1, a6=5, c6=6, b6=9, b1=6, h1=8, h2=6, c1=5, a2=8
19. Looking at d2 = 2 or 7; can More...
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Guessing is relative. It is very often the only way to do these puzzles. Just because someone offers a proof does not mean they arrived at it without guessing. Almost certainly the only way they were able to produce the proof was by trial and error - that is, making a guess and seeing how that More...
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'proved' that the second possibility was the correct one.

Some of these tough puzzles require long trial-and-error processes to solve. Today's is a case in point. You can say you used logic to solve it, but the 'trial' part of trial-and-error is by definition a guess.
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Could the B stand for brainy or brilliant!!!
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Question for you Pros: After working a puzzle and 'seemingly' solving all deductive solutions, do you folks continue 'advanced duduction' or do you attempt 'trial/error' and/or 'just plain old guessing'....?? Thx in advance for responses
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In my opinion, steps such as 17 & 19 in my posted solution are not 'trial and error.' In trial and error, you are just making a guess and runnning with it until either the puzzle is solved or you reached a point where you have made an impossible move. What I am doing is looking for a cell with just More...
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In neither instance am I taking the 'guess' to its logical solution: am I just trying to find a commonality. In abstract terms if A1 leads to B leads to C leads to D and A2 leads to F leads to G leads to D, then D is not a guess.

However, as I stated in the comments to a tough puzzle a week More...
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5:08 17th one in under 7 minutes
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15:00 even. Stopped the timer at 14 mins, got stuck: thanks, TM NoVa , for the d4=9 explanation! That makes total sense now.

PS Love the NoVa: means 'no go' in spanish, but it's also my alma mater: Villanova ('Nova)!
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