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## CHAT LOG for Tuesday, December 4, 2012

12:54 am
ElDubUC

Done, with green and a guess.
1:22 am
eyeman

Did it, like a Medium, whatever they are. (I forget)
6:28 am
tincup

done
6:35 am
GreyDragon

Go!
6:59 am
GreyDragon

Done.
7:44 am
Doll414

go
10:46 am
drwho

Difficulty score 30. No green.
10:50 am
drwho

I may have solved that by an illegitimate technique. I'll have to think about what I did and see if I can justify it.
11:00 am
drwho

Suppose you can prove cell A cannot be x implies cell B cannot be y and you can prove when cell B is not y cell A must be x. Does that mean cell A must be x?
11:02 am
drwho

Suppose that you prove that when cell A cannot be x implies cell B cannot be y and when cell B is not y cell A must be x but in either case cell C must be z. Does that mean that cell C is z?
11:04 am
drwho

I used the "technique" of assuming cell C must be z and it worked. But that may have been just a fortunate coincidence and not correct logic.
11:07 am
drwho

I think I am correct because I have covered all cases. Either cell A is x or it isn't but in either case cell C must be z.
11:09 am
drwho

However, I may not have covered all cases when cell A is x!
11:09 am
drwho

I may have only covered 1 special case where cell A must be x.
11:11 am
drwho

That is why it would really be good to answer my first question. In which case the real technique is that I have proven cell A must be x.
11:25 am
drwho

Here is the logic in simplest terms. If A implies B but B implies not A then is A true or false? Or is it not possible to say?
11:26 am
drwho

I think this is proof (or disproof by contradiction), so A is not true.
11:26 am
drwho

If so, then my new techniques are correct!
11:34 am
drwho

Actually this is not a new technique, just a n
11:36 am
drwho

...just a new wrinkle on an old technique of following an alternating inference chain until it proves impossible to solve the puzzle with the original assumption. At that point you have proven the original assumption false and can fill in the first cell in the chain with the digit you assumed did not go in that cell.
11:58 am
drwho

A little more thought and I am convinced that the 2nd technique (the one I actually used) is not correct! So I solved this one with a "lucky" guess.
12:15 pm
Lin

Oh Bleep! Just read all that and I think my head exploded. Gee thanks, 'drwho'...
1:56 pm
Ed-was_here

Go
2:34 pm
helenkeller

go
2:43 pm
Ed-was_here

Done with greens
2:44 pm
drwho

2:45 pm
drwho

The short explanation of where I went wrong is this: If A implies B that does not prove that B implies A. But that is the wrong assumption I used.
2:48 pm
drwho

In Iron Sudoku getting the right answer is all that counts. In philosophy and math correct methods are at least as important as correct answers.
3:32 pm
helenkeller

go - for real this time
3:45 pm
PandaBear

go
3:52 pm
helenkeller

done
5:38 pm
smooth_pappa

made a quick trip to Tennessee, for a funeral... 4 days to catch up on. I might not make them all tonight, but regardless... go!
6:03 pm
smooth_pappa

I just don't have it in me to finish the two experts... goodnight sudokuland!
9:58 pm
augurus

Time
9:58 pm
augurus

To
9:58 pm
augurus

Start.
10:03 pm
augurus

Finish.
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