The New Sudoku Players' Forum

[chitarup]

Hi,

I'm confused, why r6c7:3 -> r6c5:3 ->r1c5:3 ->r1c4:3 ->r4c4:3 => delete c4r8:3 is no X-Chain?

sudokuXChain1.jpg (30.35 KiB) Viewed 854 times

Please enlight me.

Best
Chitarup

[Hajime]

Hi,

I'm confused, why r6c7:3 -> r6c5:3 ->r1c5:3 ->r1c4:3 ->r4c4:3 => delete c4r8:3 is no X-Chain?

r6c7≠3 -> r6c5=3 ->r1c5≠3 ->r1c4=3 ->r4c4≠3 does not lead to c4r8≠3
So this is not a viable Xchain

[Leren]

To be more specific about your error. If r6c7 is not 3 then r6c5 is 3, but this makes 3 cells, r4c4, r4c5 and r1c5 all not 3. Thus, you can't conclude later on that r4c4 is 3, because you've already shown that it isn't 3.

Leren

[chitarup]

Hi,

I'm confused, why r6c7:3 -> r6c5:3 ->r1c5:3 ->r1c4:3 ->r4c4:3 => delete c4r8:3 is no X-Chain?

r6c7≠3 -> r6c5=3 ->r1c5≠3 ->r1c4=3 ->r4c4≠3 does not lead to c4r8≠3
So this is not a viable Xchain

Hello Hajime,

ok I understand. That is helpful. Does it mean I would need one strong link more for drawing conclusions? And in general, does it mean that you need always an even number of nodes in a x-chain?

[chitarup]

Hi Leren,

thank you.

To be more specific about your error. If r6c7 is not 3 then r6c5 is 3, but this makes 3 cells, r4c4, r4c5 and r1c5 all not 3. Thus, you can't conclude later on that r4c4 is 3, because you've already shown that it isn't 3.

Leren

[Hajime]

ok I understand. That is helpful. Does it mean I would need one strong link more for drawing conclusions? And in general, does it mean that you need always an even number of nodes in a x-chain?

Correct, also see http://forum.enjoysudoku.com/x-chain-optimalisation-t38330.html

[schroedermcken]

I don't no