dailysudoku.com

[Captain Pete]

Stuck on 7/16

17,3,9/ 6,5,2/17,8,4
685/147/29,29,3
4,2,17/3,8,9/16,5,67

279,4,3/5,29,8/67,269,1
29,179,6/479,3,14/8,249,5
5,179,8/479,129,6/249,3,27

19,5,124/49,6,3/24,7,8
8,67,47/2,17,5/3,146,9
3,679,247/8,179,14/5,1246,26

[Mogulmeister]

XY chain on 1's is a distinct possibility

[Mogulmeister]

...or if you're not happy piecing together an xy chain, there are two xy wings in there...try <47> <17> <14>

[cgordon]

I haven't even got as far as Capt. Pete. How do you get rid of the 1's in Row 8, Cols 2 & 3 ??

[Mogulmeister]

Simple box/line elimination - look at the pair of 1's in box 7 row 8 - they eliminate all the other 1's in that box.

[Captain Pete]

Herr Mogulmeister - Thanks for the hint, but I just can't seem to see a productive XY Wing. Your hint of 47-17-14 should have been enough, and it seems intuitive that those numbers should provide the key to this puzzle, but... I have a 47 in C3R8. I have 17's in common with that cell in C3R3 and C5R8. There are two 14's, but neither is in common with the cell containing 47. I do see the 74,17,14 XY Wing with 17 as the "corner" in blocks 7 and 8, but that doesn't produce any results.

[cgordon]

[Asellus]

I think you will find that the fishing is good today!

Solved it in four steps.

[Captain Pete]

CGordon, Now you're ahead of me on this puzzle. I don't see the XY Wing that eliminates the 4 in C3R8.

[Mogulmeister]

I did mention XY wings plural and outlined the first one there is another ......the XY chain blows it apart in one - making an elimiantion in Block 1.

[Mogulmeister]

cg, don't you mean row 9 col 3 ?

[cgordon]

So far - by my reckoning!

There's an xy wing with pivot 17 on R8C5 that eliminates the 4 in R9C3
(you're right Mr. M)

Then an x wing on 7s in R1 and R4

Then an xy with pivot 49 (R7C4) that eliminates 1 in R9C3

Then an xy pivot 72 in R9C3 that eliminates 6 in R9C2

That's 4 steps and I'm still not there. But then I had problems with the easy bits.

[Captain Pete]

AHA! Got it. I don't know how I missed that XY-Wing that eliminartes the 4, but that soleves it for me. Thanks Mogulmeister and CGordon. Just when I think I can't be stumped, I am.

Pete

[Captain Pete]

Actually, once the 4 is gone in C3R9, it was the XY Wing with the pivot in C9R9 eliminating the 1 in C3R3 that solves it for me.

[Mogulmeister]

This was nice - pincers in green steps in pink elimination in orange.

[cgordon]

Now you've lost me Mr M. I don't see the greens matching the nos. or positions of the pinks - and there's only one orange.

Still stuck. CG

[Mogulmeister]

cg,

The orange is the eliminated 1. The pincer cells (which also have to contain 1) are in green and you build a chain from one pincer to another.

the XY Chain. Check it out on sudopedia.

http://www.sudopedia.org/wiki/XY-Chain

[George Woods]

Mogulmeister etc.. use two XY wings
47-71-14 to eliminate the 4
followed by 76-62-27
BUT
76-62-(7) 'cos the 2 gives the pair 47 in col3 that is equivalent to a 7.

So is this a valid extension of the XY wing (I Know it is valid - but has it a name?)

[Asellus]

George,

I can't follow your argument. However, in trying to figure it out I've found something that may be closely related. It is an implication chain that includes the second XY Wing cells in its structure, though not the first. It doesn't "combine" the two XY Wings, nor does it immediately determine the <2> in R9C3, as you seem to have done. But, it is interesting nonetheless, I believe.

Here is a simplified diagram of the situation:

[jLo]