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Postby daj95376 » Tue Jan 22, 2008 6:25 am

Jasper32 wrote:Still nobody has replied to a previous post where I asked if the forcing chain of:

r8c7=5 >r8c9=7>r4c9=2>r6c8=5>r5c7<>5

is valid. I am curious if I did that correctly.

There are many more knowledgeable about chains than myself, but I'm sure that it isn't a proper chain. Your initial assertion of r8c7=5 would result in r5c7<>5 if it were true. All you've done is find a chain that agrees with the initial assertion. A chain needs to do more than that -- unless it's a continuous Nice Loop.

Since r8c7=7 is actually true, your initial assertion turns out to be false, but your elimination turns out to be true. That qualifies as Lucky.
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Postby Jasper32 » Tue Jan 22, 2008 1:55 pm

I didn't think it was correct. It made the correct removal but with a 50-50 chance of being correct, you are not sure if you were lucky or smart. I been called lucky my entire life and smart...let's not go there.

Seriously, Thank you for your help.
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re: forcing chains

Postby Pat » Mon Mar 10, 2008 5:32 pm

Steve R wrote:
Jasper32 wrote:I was wondering if the following could be a vaid chain:

r8c7=5, r8c9=7, r4c9=2. r6c8=5 then 5 could be eliominated from r5c7


The chain is OK but, as I read it, it means that, if r8c7 = 5, r6c8 = 5 and I am not clear how the elimination follows.


hey Jasper32,

in view of your later posts i must point out that Steve R was being so polite that you may have missed the point
    you listed a valid sequence of logical implications
    except at the very end you added an exclusion of 5 from a cell
    -- this exclusion has no logical basis
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