dailysudoku.com

[nataraj]

Hello everybody. This is my first time here, so pls bear with me ...

After smooth sailing I got stuck at this point:

[Johan]

nataraj,

That one step move with an xy-chain solves the puzzle completely. But if you're looking for something diffirent, there is also an xy-wing and a xyz-wing available.

[cgordon]

I see an xyz wing for 129 in R2C5, R2C4 and R5C5 that gets rid of the 9 in R1C5.

[cgordon]

P.S.

Nataraj: I'm probably missing something obvious here - but how did you solve the 19's in R8?

[nataraj]

thank you Johan and cgordon!

[nataraj]

sorry I don't remember how I did it because I'm a pencil and paper solver so once the puzzle is finished there is no traceback.

I remember I realized the naked 6 in r2c6 rather late. other than that I cant see a 9 in my PMs in C6.

[Marty R.]

I couldn't find any XY- or XYZ-Wings, but the one XY-Chain solved it, albeit I think I had a somewhat different position from the one posted.

[Earl]

I found the xyz-wing mentioned by cgordon, removing 9 from R1C5.
Then a four step xy-chain from R4C2 to R1C5, which eliminated the 3 in R4C5 and solved the puzzle.

Thanks for the tips.

Earl

[cgordon]

[Bluewing]

7's Swordfish Rows 1,3 &7 eliminates the 7 in r9c8

[shoeless]

Ok...I've been staring at this for a while, but I'm obviously missing something. I don't fully get XY chains, but XY and XYZ wings make sense to me. In any case, I solved the puzzle to this point.

[cgordon]

[Steve R]

Welcome shoeless!

You can eliminate 2 from r4c5 using the xy-wing pivoted on (19) in r5c5 with pincers r2c5 and r4c6.

Steve

[nataraj]

shoeless,

you are stuck at about the same point I was. The XY chain works as follows:

we are going to show that r4c2 cannot be 1.

if r5c1 = 1 then r4c2 cannot be 1 (both in same box)
if r5c1 = 9 (the other possibility) then a chain of inferences is set in motion:

r5c1=9 => r7c1<9>r7c1=8
r7c1=8 => r7c6<8>r7c6=2
r7c6=2 => r4c6<2>r4c6=1

but if r4c6=1 then r4c2<>1

so no matter which value r5c1 assumes, r4c2 can never be 1.
The rest is simple elimination.

Like in a XY wing, the two cells at both ends of a chain contain the same candidate "1" and therefore eliminate "1" from all cells they see.

why it says 2 at r4c6 - beats me. 2 is correct of course but becomes solved only after a few steps.

[nataraj]

thx, steve. I did it again - failed to see the xy wing

[Asellus]

cgordon,

I'm sorry to say that there is no Swordfish on 7 in this puzzle.

X-Wing, Swordfish and Jellyfish are closely related and are explained here:
http://www.sudocue.net/guide.php#XWing

For me, the puzzle yielded to a single XY-Chain that eliminates <2> from R7C6. Seems there are lots of XY-Chains in this one!

[Marty R.]

[nataraj]

[George Woods]

In solving this I found a solution that I am almost ashamed of

The 379s in Boxes 3 and 9 might easily bea DR either by removing either 3 7 or 9 from all.

So for badness postulate that r9c8 is 7 - it is not difficult to see that this makes r1c5 7 and we have the dreaded DR in 39 So r9c8 must be 9 and hence a solution

I so hated this solution that I had to look for another and finally settled on the kind of xyz wing pivoting on 123 at r4c5. Hence I almost got double value from the puzzle!

[Marty R.]