dailysudoku.com

[Bill Denholm]

I got stuck fairly early, after only 16 moves, so I asked for a hint. The move was a 4 in R1C2. I had both a 3 and a 4 in that cell and I don't understand why the 3 goes away.

Bill

[Nenthorn]

Did you find the hidden triple in column 7, Bill? It took me ages.

[Bill Denholm]

Nenthorn,

A tripple in column 7? No. In that column I have a pair of 13s and a pair of 79s. Did you mean column 8 by any chance?

[eddieg]

Column 8, look for hidden triple with numbers (3,5,9).

[Bill Denholm]

eddieg,

Darn. I see it now. I was looking the wrong way. I was counting the 3s up in R1-R3. I guess I learned something. Thanks.

Bill

[Blas]

Oh heavens, I can't see a hidden triple in c8! I have for col 8, rows 1-9:

1,3,4,6
7
3,4
3,9
3,5,9
1,3,6
8
2
3,5

which ones are in the hidden triple, please?

[TKiel]

Blas,

There is a naked (not hidden) triple in cells 4, 5 and 9 (containing numbers 3, 5 & 9).

[David]

I think you are making it rather hard. Why a naked triple ? There is a naked pair (1/6) in row 1,6 which allows the elimination of the 4 in row 1

[jabejochke]

I was stumped and I had the same problem that Bill had in looking for the '359' triple in column 8:

eddieg,

Darn. I see it now. I was looking the wrong way. I was counting the 3s up in R1-R3. I guess I learned something. Thanks.

Bill

Before recognizing the triple in column 8, I had seen the unique rectangles:

'35' base in R59C89
'13' base in R16C78

This lead me to the solution in a more drawn out manner. Only then did I see what Bill was saying to eddieg.

Jack

[TKiel]

[David]

The only cells in c8 where a 1 and 6 occur are r1 and 6. Doesn't this mean that these two cells can only be a 1 or 6 ?, hence eliminating the 4 from r1 ?

[TKiel]

David,

Yes, I now see what you are talking about. My confusion came from the fact that I thought you referred to row 1 as the location of the pair so that is where I was looking, plus the fact that it is a hidden rather than a naked pair. Also, when you said it allows for the elimination of 4 in row 1, you must have been referring only to column 8 and not the entire row, which is how I took it. So thanks for the clarification.

BTW, many people find it easier to spot naked subsets (even quads) than hidden ones (even singles), so to most of us a naked triple is easier to find than a hidden pair.

[Victor]

David is quite right of course, though I think the 16 pair would be called hidden by most people, though I don't see that titles matter very much. If you're doing it computer-style, working with candidate lists, then you don't see just 1 & 6 in the two positions, you see 1346 and 136. The 16 pair is 'masked' or 'hidden' by the other numbers - hence the name.
The point about hidden multiples is that you can remove the chaff from the relevant boxes, in this case the two 3s and the 4. On the other hand, if you spot the naked triple 359, then you can remove any of these numbers that appear in other boxes.
(Oddly enough, if you're a computer you might choose to see a naked quad - 3459 in rows 3, 4, 5,and 9, thereby allowing you to delete the 3s and 4 from the bixes that contain the 1 & 6.) (Is that a sort of number pun or something? - the repeated 3,4,5,9 i mean)

[TKiel]

Names of techniques do matter in the sense that using the correct name allows others to understand what one did at a certain point in the puzzle. When David said there was a naked (1,6) pair that allowed the exclusion of a 4, it made no sense to me and that's one reason I said I didn't see it. (The other was confusion about where it was, which was mostly my fault. Most of the discussion had been centered on column 8, and that's what he was referring to, but I didn't make that connection). His explanation made it clear that he was referring to both column 8 and a hidden pair.

[David]

Yes, my apologies it was indeed a hidden / masked pair. Anyway an interesting puzzle. Obvious when you spot the solution, infuriating when you can't.