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Did anyone solve this by anything other than trial? I see that R7C9 cannot be a 7, because of the way it relates to R7C5, R9C4 and R9C9; but it don't know why.

R1C3 - R1C4 - R2C5 make a Y wing. R2C3 cannot be a 4.

Thanks, I didn't see that one.

Y Wing in R4C2 (25), R5C1 (5 Cool

, R5C9 (2

eliminates 2s in R4C8 and R4C9

Did anyone solve? I found the Y wing: R2C1(1 Cool

, R2C5(3

, R3C6(13) eliminates 1 in R3C3, but didn't get any further.

The a, b, c below form a "Y" wing. x cannot be a 4.

+-----------+----------+-----------+
| 159 19 59 | 4 3 7 | 8 2 6 |
| 4 2 6 | 1 8 9 | 7 3 5 |
| 8 7 3 | 56 5 ...

+----------+----------+--------+
| 3 279 4 | 8 79 6 | 27 5 1 |
| 8 a27 1 | x27 4 5 | 6 9 3 |
| 5 6 b79 | 1 3 c29 | 27 4 8 |
+----------+----------+--------+
| 7 4 6 | 9 5 3 | 1 ...

Also, Y wing in R1C9, R3C7, R5C7 removes <8> from R1C7.

Interestingly, a 3 must be in R5C5 or you would have a rectangle of "68'S", which is not allowed in a solvable puzzle.

r2c7 must be a 3; otherwise you have a UR in R3c27 and r4c27.

I used the 169 XY Wing at r27c7,r9c9 (-1r12c9) which solved it.

Thanks!

Y wing in R8c1, R8C9 and R5C9 eliminates 8 from R5C1

Y wing - r1c7, r3c6, r3c8 eliminates 6 in R1c5, r1c6 and r3c7

Y wing - r4c6, r4c8, r5c7 - eliminates 4 in r5c4 and r5c6

Y wing - R4C3, R7C3, R9C1 Eliminates 2 in R5C1

Y wing - hinge r9c3 - r7c6 = 1

I used a even number 69 chain starting with R1C3 and ending in R5C2. The result is that R1C2 cannot be a 6 or a 9.

Thanks!

Thanks. Very clever. I would not have found that.

OK, I see that eliminating the "2" from R3C4 solves it, but how did you know to eliminate the "2". Was it a try one and if that doesn't work, it's the other one?

Thanks Tom. I missed it!