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Hi,

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



Please enlight me.

Best
Chitarup

chitarup wrote: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

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 wrote:

chitarup wrote: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?

Hi Leren,

thank you.

Leren wrote: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 wrote: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

I don't no