Anette wrote:Is this cheating?

I have started out with the “Very Hard” sudoku from Times like this:

*43*8*25*

6********

*****1*94

9****4*7*

***6*8***

*1*2****3

82*5*****

********5

*34*9*71*

After solving according to logic so far, I ended up with the following:

*4398*25*

6**425***

2****1*94

9****4*7*

3**6*8***

41*2*9**3

82*5*****

****4***5

53489*71*

Then I could see no more “simple” logic ways to solve it, so I started looking at the 2 possibilities in Column 1 and did the following:

Option A: If R1C1 = 7, then 7 can go nowhere else in Row 1. For R1C6, the only possibility is then 6

Option B: If R1C1 = 1, then R8C1 has to be 7. Then R8C4 has to be 1. Then R3C4 has to be 7. Then R1C6 cannot be 7, and the only possibility for it is 6.

So either way, R1C6 had to be 6, and from there, I could solve the puzzle.

Is it considered cheating to set up 2 alternatives like that? I did draw some rings and squares around the pencil marks, but might as well have done it in my head since the chain wasn't that long.

/Anette

No, it isn't cheating. -- You solved the puzzle using only your brain.

No, it isn't trial and error. -- You made no trial and found no contradiction.

No, it isn't guessing. -- You *certainly* didn't guess.

You simply proved the contents of a cell by clear, reproducible, straightforward, logic.

I realize I'm responding to an older post, but we've it we've been talking about this elsewhere. It seems that this idea comes up again and again, but often gets shot down.

Certainly, if you can do it in your head, you simply have no choice but to use it -- you can't simply pretend you don't see the answer. And if you are already using pencil marks, it just a matter of degree how much information you can cram into each cell.

Animator wrote:The technique you are missing in your example-grid is an X-wing in the number 6.

I might as well say that if instead you had solved by searching and searching until you found the X-wing, you would have missed solving the grid by the Forced Chain Proof.

It seems that if one cannot put a name to the tactic they use, cannot describe its exact parameters, form and function -- they're just guessing.

See:

http://forum.enjoysudoku.com/viewtopic.php?t=692http://forum.enjoysudoku.com/viewtopic.php?t=594