## What is the "Digit Rule"?

Post the puzzle or solving technique that's causing you trouble and someone will help

### What is the "Digit Rule"?

Hi All,

I try to solve the daily Sudoku at sudokuhints.com.
I can understand and use all their suggested solving techniques but sometimes it comes up with a hint that refers to the "Digit Rule".
Even if I let it fill in the specific number, I can't understand why it is correct as I'm unab;e to exclude other possibilities for the same number.
I can't find anything on this on Google either.
However, it may have something to do with the sum of the region (row, column or block) must be 45 and therefore there may be some exclusion rules.
Spent days on trying to figure this out...

1. could the "Digit Rule" be known by another name?
2. can anyone explain the logic to me or refer me to a link that explains it?

Rene
RenoirIII

Posts: 3
Joined: 24 October 2016

### Re: What is the "Digit Rule"?

I've never heard of the Digit Rule. If you gave us a specific example of where they apply it I am sure we could figure it out.

JasonLion
2017 Supporter

Posts: 640
Joined: 25 October 2007
Location: Silver Spring, MD, USA

### Re: What is the "Digit Rule"?

Hi,

Thanks for trying to assist...

I have attached a graphic.

The rule applies to adding a 7 to r5c5

I hope this helps...

Rene
Attachments
digit rule
digit-rule.png (93.55 KiB) Viewed 1831 times
RenoirIII

Posts: 3
Joined: 24 October 2016

### Re: What is the "Digit Rule"?

Sorry,

That was too simple.
In the first graphic it was simply the only possibility.
But look at the second graphic where the system suggests "Put a 5 in box 8 at r8c5 (Digit Rule)"

Rene
Attachments
digit_rule_2.png (54.65 KiB) Viewed 1831 times
RenoirIII

Posts: 3
Joined: 24 October 2016

### Re: What is the "Digit Rule"?

If you assume that r8c5 is 2 and follow along what that implies for the rest of the puzzle you come to a contradiction fairly quickly. So r8c5 does need to be 5. However that is a fairly complex technique. All that is required to solve the last puzzle is naked pairs, locked candidates, and singles, so it is difficult to see them resorting to Nishio (follow the implications of assuming a cell contains a specific digit and check for contradictions along the way).

Based only on the first example, it seems like Digit Rule is what we call Naked Single, only one digit is valid in the cell (all others are directly contradicted by already placed digits).

The second example is a little more complex, as there is a very simple move readily apparent. By Full House r2c3 must be 1. If that isn't mentioned it makes little sense to talk about r8c5. If r2c3 wasn't mentioned, perhaps there are several steps missing before you get to r8c5. In several simple steps you could easily get to a situation where r8c5 becomes a Naked Single.

JasonLion
2017 Supporter

Posts: 640
Joined: 25 October 2007
Location: Silver Spring, MD, USA

so, their "Cell Rule" is what we call "hidden single",
and their "Digit Rule" is what we call "naked single"

Pat

Posts: 3674
Joined: 18 July 2005