## What's this?

Advanced methods and approaches for solving Sudoku puzzles

### What's this?

In the following pattern R2C8 and R7C9 allways have the same value.
I used some kind of combination between XY wing and this to exclude "<9>"

Code: Select all
` *--------------------------------------------------------------------* |                      |                      |                      | |                      |               <9>    |        79     789    | |                      |                      |               789    | |----------------------+----------------------+----------------------| |                      |                      |                      | |                      |                      |                      | |                      |                      |                      | |----------------------+----------------------+----------------------| |                      |               37     |               79     | |                      |                      |                      | |                      |               39     |                      | *--------------------------------------------------------------------*`
evert

Posts: 186
Joined: 26 August 2005

Hi Evert.

I would made that deduction with a discontinuous nice loop:

[r2c6]-9-[r9c6]-3-[r7c6]-7-[r7c9]-9-[r2c9|r3c9]-7-[r2c8]-9-[r2c6], => r2c6<>9.

Regards, Carcul
Carcul

Posts: 724
Joined: 04 November 2005

### Re: What's this?

evert wrote:In the following pattern R2C8 and R7C9 allways have the same value.
I used some kind of combination between XY wing and this to exclude "<9>"

You can look at that as a chain of almost-locked-sets:
A = {r79c6} = {379}, where r9c6<>9 implies r7c6=7
B = {r7c9} = {79}
C = {r23c9} = {789}, where r23c9<>9 implies r23c9=78 (naked pair)
D = {r2c8} = {79}

Chained: if r9c6<>9 then r2c8=9, and v.v.

Ron
ronk
2012 Supporter

Posts: 4764
Joined: 02 November 2005
Location: Southeastern USA

### Re: What's this?

evert wrote:In the following pattern R2C8 and R7C9 always have the same value.
I used some kind of combination between XY wing and this to exclude "<9>"

Code: Select all
` *--------------------------------------------------------------------* |                      |                      |                      | |                      |               <9>    |        79     789    | |                      |                      |               789    | |----------------------+----------------------+----------------------| |                      |                      |                      | |                      |                      |                      | |                      |                      |                      | |----------------------+----------------------+----------------------| |                      |               37     |               79     | |                      |                      |                      | |                      |               39     |                      | *--------------------------------------------------------------------*`

You see a set of size 6 with digit candidates 3789 with maximal multiplicities 1213 for a total of 7 so any outside choice that would reduce the total by 2 can be eliminated. And your <9> does reduce the max multiplicity of 9 in the set from 3 to 1.
aeb

Posts: 83
Joined: 29 January 2006

aeb, I have to say that I like the way that your concept of a single set and multiplicities simplifies ALS work. I think you ought to start your own thread on the subject.
Myth Jellies

Posts: 593
Joined: 19 September 2005

Myth Jellies wrote:aeb, I have to say that I like the way that your concept of a single set and multiplicities simplifies ALS work. I think you ought to start your own thread on the subject.

OK - done.
aeb

Posts: 83
Joined: 29 January 2006