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Skyscraper on 4 in rows 2 and 9 is all that is necessary.

I was looking at the basic techniques on the Sudopedia mirror to put names to the techniques I use. I don't really understand how Scanning is different from Cross Hatching. There seems to be an imp ...

Interesting how the definition of "Very Hard" evolves.
The wife and I were discussing the same thing.
And, I hope, you were talking about Sudoku Laughing

ROFL!!

I agree completely. On the average, I find hard puzzles more difficult than very hard puzzles. The VH puzzles involve more advanced techniques, but those techniques are generally easy to spot once ...

After the 248 xy wing, there is a naked quad and the puzzle unravels easily after that.

Here is the puzzle after basics.

+-------------------+--------------+---------------+
| 1245 13489 124 ...

248 xy wing did it for me.

I too like to avoid uniqueness based solutions.

The 679 xy-wing is actually two steps, 1) 7 x-wing 2) 679 xy-wing.

The 367 xy-wing is a one stepper that avoids uniqueness tests.

23-5 xy wing is another one stepper, though it unravels slower than typical after the xy-wing.

Edit: That was for the Jan 23 puzzle. The Jan 25 puzzle wasn't even available when I posted this.

I don't see the 39 UR. After the basics, I had:

+--------+-------------+-------------+
| 5 8 9 | 4 36 1 | 7 36 2 |
| 3 7 4 | 69 2 5 | 69 8 1 |
| 6 2 1 | 39 8 7 | 5 ...

I checked today, and the numbers are back in their boxes. *shrug*

Starting today, the numbers in the play online grid don't fit in the boxes. The big numbers are clipped off at the bottom and the pencil marks bleed into the next box (see below). Any idea what is c ...

That's odd. I'm still seeing the Nov 13 puzzle as the most recent puzzle.

If you really want to use xy wings, it takes 3:

-169 xy-wing (or 16-9 xy-wing)
2-69 xy-wing
-489 xy-wing

158 xyz-wing solves it in one step.

I would call that a pincer transport since the 8 was transported, but my definition of a pincer transport is more liberal than others. You could also call it pincer coloring.

You could also use t ...

You made a mistake somewhere prior to your picture. Some of your numbers conflict with the solution to the Apr 16 2008 puzzle.

PS If you use the "Play Online" button on this site, you ...

It does not appear that you can add "pencil marks." Without pencil marks, hard puzzles would be nearly impossible.

257 xy-wing
finned x-wing (6)

For something different there is a:Bug+2 than says r5c8<>8

I do not see how the Bug+2 can eliminate 8 from r5c8. If I understand Bugs correctly, the Bug+2 says that r6c3=4 or r7c2=8. From ...

After the basics, I had:

+---------------+-------+----------------+
| 1 457 45 | 9 2 8 | 47 6 3 |
| 479 8 49 | 5 3 6 | 1 247 247 |
| 23 23 6 | 1 7 4 | 9 58 58 ...