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Free Press Jan 22, 2010
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Sat Jan 23, 2010 7:20 pm    Post subject: Reply with quote

keith wrote:
daj95376 wrote:
Let's split a few more hairs. Sashimi X-Wing, finned X-Wing, Skyscraper, 2-String Kite, turbot fish, and Empty Rectangle are all simple coloring ... if ... you allow coloring on grouped strong links.
Really? I'll have to think about it.

Does this include both ER cases, where the hinge pin cell does / does not contain the candidate?

The reason I hesitate is because I don't think grouped coloring is bi-directional. For example in simple coloring I might be able to say: If cell A is true then cell B is false.

The reverse statement is valid: ... and then if B is false A is true.

In grouped coloring I am not sure the reverse statement can, in general, be made. Even so, does that matter in the patterns you have named?

Yes on ERs. However, there are other techniques besides the Empty Rectangle -- like the 2-String Kite -- when the hinge cell must be empty.

I went through a very painful discussion on ERIs in the Players' Forums awhile back. They introduced me to a concept on bi-directional links that still smarts (and I don't completely accept). I'll show how it works ... if you realllllly insist.

Grouped coloring doesn't have to be bidirectional. All that matters is the color of the cells at the endpoints of the chain ... and any cell that sees them. Grouped coloring has been around for a long time in the form of X-Colors and other coloring techniques based on grouped coloring.

Regards, Danny
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keith



Joined: 19 Sep 2005
Posts: 3182
Location: near Detroit, Michigan, USA

PostPosted: Sat Jan 23, 2010 9:06 pm    Post subject: Reply with quote

Quote:
I went through a very painful discussion on ERIs in the Players' Forums

I stay away from that forum. For some of the participants, the size of their egos is far larger than the substance of their discussion.

Directionality of a link is my own idea which I have not discussed with anyone else. I have no idea if they mean the same thing that I do.

Since I am not a programmer, and I argue the logic each time, the precise names, rules and formulas do not matter to me. The example of directionality I like is that of the half M-wing.

In the regular M-wing you start with two bivalue cells that have the same candidates.
A ..... B
XY .... XY

Suppose you can prove they have the same value: If either one is X, so is the other. They are a complementary pair. Then, you can build the M-wing by adding a strong link in Y at either end.

The half-wing occurs when you can only say that if A is X then B is X. (You cannot say that if B is X, A is X.) Then, you can only add the strong link in Y at B.

Keith
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cgordon



Joined: 04 May 2007
Posts: 769
Location: ontario, canada

PostPosted: Sat Jan 23, 2010 11:16 pm    Post subject: Reply with quote

Hey: Even though I can't even copy a Sudoku correctly - at least my screw-up generated a discussion. And at least I am the only one who can spell colouring.
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daj95376



Joined: 23 Aug 2008
Posts: 3855

PostPosted: Sat Jan 23, 2010 11:26 pm    Post subject: Reply with quote

cgordon wrote:
Hey: Even though I can't even copy a Sudoku correctly - at least my screw-up generated a discussion. And at least I am the only one who can spell colouring.

Laughing Laughing Laughing

Thanks Craig, I needed that!
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strmckr



Joined: 18 Aug 2009
Posts: 61

PostPosted: Tue Jan 26, 2010 1:48 pm    Post subject: Reply with quote

nice. Smile

coloring (American)
colouring (English / Canadian )
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