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May 28 2005 very hard

 
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hellohello
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PostPosted: Mon Dec 12, 2005 7:13 pm    Post subject: May 28 2005 very hard Reply with quote
I was going back through the archives pulling some of the "very hard" puzzles. I got to this one, and am completely stuck. I know what number is to go next, but Idon't know WHY. After I have put in 13 of my own numbers, the "next' logical number (according to the hint) is that a 7 should be placed in the 4th column 2 square down. I can't understand why. Could anyone explain? Thanks!
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado
PostPosted: Mon Dec 12, 2005 8:25 pm    Post subject: Is this the answer you're looking for? Reply with quote
I'm not sure exactly what the grid looks like at the point where you're stuck, but maybe this previous discussion will shed some light on the hint. dcb
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hellohello
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PostPosted: Mon Dec 12, 2005 10:50 pm    Post subject: Reply with quote
Thanks David, it did help Very Happy
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alanr555



Joined: 01 Aug 2005
Posts: 198
Location: Bideford Devon EX39
PostPosted: Sat Dec 17, 2005 2:04 am    Post subject: Reply with quote
Code:

It was possible to get a fair way with this one using Mandatory
Pairs but that method has an "Achilles Heel" in that it does not
easily spot "remote" pairs without recourse to the compilation
of "Candidate Profiles". However, having recorded the C/Ps
the M/P data can expedite the subsequent solution.

I found that the key was discovering that r3c1 and r3c9 formed
a remote pair. Eliminating those values l4ed to a solution for
r3c4 and then for r3c6. This opened up the puzzle quite a bit
and allowed considerable progress from that point - certainly
well beyond thirteen cells, the limit reached by the initial enquirer.

Alan Rayner  BS23 2QT
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