dailysudoku.com

[nataraj]

This is where I got with basic moves:

[tippwell]

45 in r9c6 along with r7c4 and r9c7 eliminates some 8s in boxes 8 and 9

[TKiel]

I made the same exclusion as nataraj but saw it as a finned X-wing.

[sdq_pete]

There's an XY wing with pivot at R9C6 which eliminates 8 from R9C4 - however it doesn't open the puzzle.
I reached the following position:

[George Woods]

Using Peter's position, I was intreagued by the quad of 28,28,28, and 128 and thinking that this was a potential UR, I realised it is a false one (Unfortuately if one presses ahead and puts a 1 in r8c3 - a solution emerges- but this is yet another lucky mistake)

However looking at the 28s it seems very clear that a 2 in r8c9 leads to a 2 in r6c3 and so a 2 in r8 c2 Oh dear two 2's in row 8 Hence r8c9 must be 8 and it all falls out.

Once again I haven't seen how to transpose this into a standard move!

Looking again at the pattern of 28s They almost form what I might call "Gift wrapping" with 28s tying the imaginary parcel with tails both of which uses all the available cells for 2 in the box, Hence 2 is not allowed on the same line as the "tail extension" - I find this easier to visualise than to describe!

[Marty R.]

I also couldn't find any wings, but the skyscraper on 2 did the job.

[sdq_pete]

[Marty R.]

[KSipher]

Marty

This is where I am in this puzzle. Could you possibly explain the skyscraper - I thought I understood them, but I cannot follow it in this puzzle.

Thanks so much
Kathy

[isabel]

[sdq_pete]

[nataraj]

many thanks, isabel, for pointing out the wings!

seems like, yet again, at some crucial point there are many different ways to solve the puzzle.

And yes, I am not quite sure about the correct termnology of the logic I used.
Basically I like to call it an alternating inference chain, which it is for sure, but then again, the reasoning uses only one digit ('2') so it could also be called "coloring", couldn't it? But on the other hand, coloring usually refers to strong links only, right? I am very confused, could someone please clear things up?

[cgordon]

There's a fairly easy to spot Empty Rectangle (ER) using 5's.

There are only two 5's in C6. These line up with L shaped "hinges" of 5s in both Boxes 6 & 9 (only one hinge is needed for an ER). Check this out! It doesn't matter which of the two candidates in C6 are 5s - the "hinges" ensure that there cannot be a 5 in both R4C8 and R9C8.

Easy steps from there.

[dpm]

[cgordon]

.../actually I redid this and found the 5 in R4C8 was taken out by a naked triple and that my ER, although correct, did not offer an easy solution - I must have erred somewhere. However, since I am into ERs there is another one on 2's that takes out the 2 in R8C2. Now it's easy to finish !!

[TKiel]

[Asellus]

Regarding all the skyscraper comments... perhaps I can shed a little light from my own experience.

When I started reading this board, I saw reference to "Skyscrapers" and "Kites" and "Turbot Fish" and thought, "Oh boy! New things to learn."

When I figured out what they were, I was very disappointed because I already knew them all. They all are really the same thing: simple colorings that can be done in ones head. They differ only in their geometries

All involve three end-to-end links on a single digit in either of the following two configurations:

X-strong-X-strong-X-strong-X
X-strong-X-weak-X-strong-X

If the strong links on the ends are parallel: "Skyscraper".
If the strong links on the ends are perpendicular: "Kite".
If the strong links on the ends are at an angle: "Turbot Fish".

Or, that's at least how the words are usually applied, it seems to me. But the names aren't always used consistently.

About the logic...

If all three links are "strong" (i.e., either/or conjugate pairs), then the relationship between the pincer ends is also conjugate: either one or the other is true, but not both. (As an aside, this can be seen as simple basic coloring.)

If the middle link is "weak" (i.e., at most one is true and both can be false), then the relationship between the pincers is what is somethings called "strongly inferential": one or both can be true. (This can be seen as what is called "multi-coloring" or "color wing" involving a weak link "bridge.")

nataraj's example is of the second sort (and would often be called a "kite").

[Edit to clarify logic description.]

[KSipher]

Once again, thanks for the help. I was able to finish the puzzle without needing to use a skyscraper, but I would still appreciate anyone explaining how to apply this method at the point I was stuck at (above.) I would love to add this to my 'skills.' Thanks again!
Kathy

[Earl]

A curiosity.

The skyscraper in <2's> which eliminates <2> from R6C3 is a double!
Both R4,9 or C2,9.

Earl

[Asellus]