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[ZeroAssoluto]

Hi everyone,

[TomC]

the 234 wing? in r5c7, r6c8, r9c7 gives -3 in r4c79

[ZeroAssoluto]

Hi TomC

it's a XYZ-Wing and delete number 3 only in r4c7.

Ciao Gianni

[TomC]

Hi Gianni,

If you use those 3 cells, then a 3 in r4c9 gives r9c7 = 3 which means no 3's in box 3

I questioned the type of wing as it seemed a little different to a XYZ as it eliminated both 3's

Tom

(You could also use the 34 W wing to delete the 3 in r4c9)

[ZeroAssoluto]

Hi Tom

If you want to use a Wing technique (XYZ-Wing in this case) the rule says that you can delete the numbers only in the target cells (which are those that are "viewed" from the three cells you use for XYZ-Wing).
R4C9 is not "view" from R9C7.

If you don't want to use a wing, but other techniques or attempts, you can find some numbers to be eliminated, such as the number 3 in R4C9;

as with the W-Wing I didn't use because I was just looking for solutions in one step.

Ciao Gianni

[Mogulmeister]

Interesting. In the standard definition of the XYZ wing (as I understand it) you can only remove 3 in r4c7 just working with the logical 234 structure at r59c7 and r6c8.

What I think you may be describing Tom is the extra elimination which comes about because of this puzzle's structure rather than the logic of the standard XYZ wing.

Let's look at the (34) in r6c8 .

If it's 4 then r59c7 form a 23 pair eliminating only the 3 at r4c7. According to the cells of the XYZ. However due to the layout of this puzzle that would also eliminate the 3 in r2c7. This means that one of the 3's in r12c9 is true and so, additionally the 3 in r4c9 is also eliminated.

If it's 3 those two cells r4c79 also lose their 3's.

You can do the same with the (23) in r9c7.

If it's 2 then naked pair (34) r5c7 and r6c8 is formed and both the 3's in r4c79 are eliminated.
If it's 3 then the XYZ only eliminates the 3 in r4c7 but coincidentally the 3 in r2c7 is also removed. As above, this means r12c9 must contain 3 and r4c9<>3.

I think you might want to call this a Bonus XYZ wing ?

[TomC]

Thanks all for the replies

I was just trying to share my logic to solve, I just go as I see it, not worrying too much about technique (but always learning)

Maybe a hybrid XYZ like a car with two motors

Tom

[Mogulmeister]

Imho it's good that you do it that way Tom.

An unconventional approach can sometimes really break through. This thread reminded me of one that took place -cough- almost exactly 14 years ago.

It was a thread started by Earl with some very detailed contributions and I stuck a picture of a simplified solution (11th post in) that surprised a few.

http://www.dailysudoku.com/sudoku/forums/viewtopic.php?t=1955

[dpm]

[dpm]

[hughwill]

Yes the X wing on 1s r18 -1r6c3 solves it in one.

As does the UR on 47 r46 r6c1=1