The New Sudoku Players' Forum

[9X9]

Is it me, or is the definition of a Hidden Subset in the "Sudoku > Solving Techniques" section of the SadManSoftware.com 'site incorrect?

[MCC]

I think it's you. The definition looks ok to me. If you think there is a problem why don't you spell it out either for confirmation or further elaboration of the term.

[9X9]

For Hidden Subsets simes says, "...... then those candidates can be removed from other cells in that row, column or block".

This is identical wording to the definition given there for Naked Subsets. There is also a subsequent identical mis-spelling of "than" as "that".

[Pat]

Is it me, or is the definition of a Hidden Subset in the "Sudoku > Solving Techniques" section of the SadManSoftware.com 'site incorrect?

yes, good catch!
the brief text at www.sadmansoftware.com/sudoku/solvingtechniques.htm
is wrong:

{ edit: quoted at the time, has been corrected }

Hidden Subset
If two cells in the same row, column or block have only the same two candidates, then those candidates can be removed from other cells in that row, column or block. This technique can also be extended to cover more that two cells.

but the full explanation at Hidden Subset is fine.

- Pat

[9X9]

Pat - yep, that was my take too and it might be contributing to "newbie confusion". I'll point simes at it.

MCC - is that another plastic goldfish? If so, could you make it a female this time - don't want tso getting one of his faces on!!!

[simes]

9x9. Thanks for letting me know, I've just corrected the page.

S

[9X9]

simes - if you remain in correcting mode and mood, the minor residual point is that the Naked Subset definition still says, "This technique can also be extended to cover more that (sic) two cells."

[simes]

Tis done. Thanks again

S

[Ruud]

Simon,

while you're at it,

this coloring example has led to confusion with some people:

Code: Select all

  1  |     |     
    1|     |     
     |     |     
-----+-----+-----
1    |     |  1 
1 1 1|     |     
1    |     |    1
-----+-----+-----
     |     |     
     |     |     
     |     |     

You have colored it this way:

Code: Select all

  a  |     |     
    A|     |     
     |     |     
-----+-----+-----
-    |     |  1 
- A a|     |     
-    |     |    1
-----+-----+-----
     |     |     
     |     |     
     |     |     

But it can also be colored this way:

Code: Select all

  1  |     |     
    1|     |     
     |     |     
-----+-----+-----
a    |     |  A 
- - -|     |     
A    |     |    a
-----+-----+-----
     |     |     
     |     |     
     |     |     

Which, combined, leads to the conclusion that this may not be a valid puzzle at all.

Notwithstanding these minor glitches, you explanations are amongst the best on the net.

Ruud.

[simes]

Good point, I hadn't noticed that. Thanks for bringing it to my attention. I'll see if I can come up with a better example.

Notwithstanding these minor glitches, you explanations are amongst the best on the net.

Thanks. People either seem to find them helpful, or complain they don't understand them. (But then I guess those who fall in the middle and find them acceptable, don't feel the need to get it touch.)

Simon

[9X9]

I'm with Ruud.

[emm]

simes, your site is an excellent source of information, I use it frequently. I found angusj's easier when I was starting off but yours is great for advanced techniques - you've made a lot of things clearer for me. Thanks.

[simes]

Folks, thanks for the ego restoration:D It's hard to judge how clear an explanation is when you've written it yourself.

I think I can fix that colouring example simply by adding a few more candidate 1s to prevent the alternative colouring.

Code: Select all

  a  |     |     
    A|     |     
     |     |     
-----+-----+-----
-    | 1   |  1 
- A a|   1 | 1   
-    |  1  |    1
-----+-----+-----
     |     |     
     |     |     
     |     |     

Is that better?

Simes

[angusj]

Is that better?

I'm afraid it's still confusing. Removing the 3 candidates marked with a dash in box 4 will leave column one without any 1 candidates. Also, by using a simpler technique (I think you call it a box-column interaction) you could remove the 'conjugate' candidates instead in box 4.

[simes]

well come to that, it would also leave boxes 7, 8 and 9 without any 1s. It's a partial example, meant to illustrate a point, but perhaps it needs to be more.

I'll think on it.