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[ZeroAssoluto]

Hi everyone,

XY-Wing 1,2,8 in r58c9,r7c8 and -8 in r46c8
or
Skyscraper with number 1 in r37c5,r38c9 and -1 in r7c78,r8c4

Ciao Gianni

[TomC]

[TomC]

Is a skyscraper the same as colouring?

[immpy]

Hello Tom. A Skyscraper is a special form of Turbot Fish and it can be seen as two Sashimi X-Wings. The description of the pattern sounds more complicated than it really is: Concentrate on one digit. Find two rows (or columns) that contain only two candidates for that digit. If two of those candidates are in the same column (or row), one of the other two candidates must be true. All candidates that see both of those cells can therefore be eliminated.

cheers...immp

[immpy]

The digit here is 1. And the columns are c5 and c9. 1 appears only twice in each of these columns. The offset ends of the pattern are what make the potential eliminations, in this case cells r7c5 and r8c9. These act as pincers on 1, as one of these cells must equal 1 based on the pattern. All cells that can see both of these cells will be <>1. 1 can therefore be eliminated in the cells that Gianni has noted.

cheers...immp

[TomC]

Thanks for that immpy.

The way I saw the solution was if r8c4 = 1 then r3c9 = 1 and that leads to no 1's in box 2

iechyd da

[Mogulmeister]

[Mogulmeister]

[Mogulmeister]

...and of course it is a chain as well.

(-1)r7c5=(1)r3c5-r3c9=(1)r8c9 so r8c4<>1

In English:

"It isn't 1 at r7c5 so must be 1 at r3c5 isn't 1 at r3c9 must be 1 at r8c9".

The logic always alternates between the " - "(isn't) to "=" (must be).

Usually there is a bracketed number or numbers just to the left of the cell reference to let you know what is going on. The above example is simple as we are only on digit 1. Where there is no bracketed number the chain assumes you are still on the same digit. I didn't really need the (1) quite so much above.

You will see in some of the more involved chains that there is a transition to another digit as in the example below:

(1=4)r4c2-(4=3)r8c2 etc

In English:

"Not 1 but must be 4 in r4c2 so not 4 but must be 3 in r8c2 etc"

This is for when you move from one strong linked digit to a different one.

[Mogulmeister]

….finally Tom you showed the destruction of all 1s in box 2 if r8c4 = 1. It also causes another major contradiction. If you plug 1 into r8c4 and follow the strong links around in the diagram it will end up putting two 1’s into box 8.

[Mogulmeister]

[TomC]

Thanks for all of this Mogulmeister

Very appropriate solutions following our opening match (All the 1's)

Tom

[dongrave]

Excellent job explaining the Eureka expressions in English mogulmeister! I had a tough time learning Eureka until one day I began thinking of them in the English terms that you explained.

[Mogulmeister]

Thanks Don.

You just explained exactly my own Eureka moment.