## Help with forcing chain problem

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

### Help with forcing chain problem

I have read just about everything there is on the subject of forcing chains but this puzzle has me stumped.

I am afriad to use any notation but I can tell you the cells and the values I assigned to each.

Hopefully, someone can help me.

The forcing chain in question is:

r5c2=2 r5c3=8 r5c9=9 r4c8 r4c4=9 r4c2=7

I thought since the beginning call was a 2 and the ending cell was a 7 there was no conflict and that r5c2 should equal 2....not so. what is the error of my thinking???

*-----------*
|..4|...|..6|
|.3.|.5.|4..|
|..7|.21|..3|
|---+---+---|
|..3|..6|..4|
|...|...|...|
|9..|8..|7..|
|---+---+---|
|3..|27.|9..|
|..1|.9.|.4.|
|7..|...|8..|
*-----------*

*-----------*
|..4|38.|1.6|
|13.|65.|4..|
|..7|421|5.3|
|---+---+---|
|..3|.16|2.4|
|4..|.35|61.|
|916|842|735|
|---+---+---|
|385|274|961|
|..1|598|347|
|749|163|852|
*-----------*

*--------------------------------------------------*
| 25 259 4 | 3 8 79 | 1 27 6 |
| 1 3 28 | 6 5 79 | 4 27 89 |
| 68 69 7 | 4 2 1 | 5 89 3 |
|----------------+----------------+----------------|
| 58 57 3 | 79 1 6 | 2 89 4 |
| 4 27 28 | 79 3 5 | 6 1 89 |
| 9 1 6 | 8 4 2 | 7 3 5 |
|----------------+----------------+----------------|
| 3 8 5 | 2 7 4 | 9 6 1 |
| 26 26 1 | 5 9 8 | 3 4 7 |
| 7 4 9 | 1 6 3 | 8 5 2 |
*--------------------------------------------------*
Gee

Posts: 50
Joined: 18 March 2007

Gee wrote:I have read just about everything there is on the subject of forcing chains
but this puzzle has me stumped.

The forcing chain in question is:
r5c2=2 r5c3=8 r5c9=9 r4c4=9 r4c2=7
I thought since the beginning call was a 2 and the ending cell was a 7 there was no conflict and that r5c2 should equal 2....not so. what is the error of my thinking???
Code: Select all
` *-----------* |..4|...|..6| |.3.|.5.|4..| |..7|.21|..3| |---+---+---| |..3|..6|..4| |...|...|...| |9..|8..|7..| |---+---+---| |3..|27.|9..| |..1|.9.|.4.| |7..|...|8..| *-----------* *-----------* |..4|38.|1.6| |13.|65.|4..| |..7|421|5.3| |---+---+---| |..3|.16|2.4| |4..|.35|61.| |916|842|735| |---+---+---| |385|274|961| |..1|598|347| |749|163|852| *-----------*  *--------------------------------------------------* | 25   259  4    | 3    8    79   | 1    27   6    | | 1    3    28   | 6    5    79   | 4    27   89   | | 68   69   7    | 4    2    1    | 5    89   3    | |----------------+----------------+----------------| | 58   57   3    | 79   1    6    | 2    89   4    | | 4    27   28   | 79   3    5    | 6    1    89   | | 9    1    6    | 8    4    2    | 7    3    5    | |----------------+----------------+----------------| | 3    8    5    | 2    7    4    | 9    6    1    | | 26   26   1    | 5    9    8    | 3    4    7    | | 7    4    9    | 1    6    3    | 8    5    2    | *--------------------------------------------------*`

yes, there is no conflict in this chain

therefore, r5c2 could equal 2
( as far as this chain is concerned )
"could" does not prove "should"

Pat

Posts: 3551
Joined: 18 July 2005

### Forcing Chain

I guess I was under the false impression that if the beginning and ends of the chain terminated, in this case block 4, and there were no conflicts that r5c2=2 would be correct. Back to the drawing board!
Gee

Posts: 50
Joined: 18 March 2007

Gee,

There is an xy wing that will solve the puzzle.

dan
dan

ArkieTech

Posts: 2867
Joined: 29 May 2006
Location: NW Arkansas USA

### Forcing Chain

Thanks Dan. I missed that in my quest to find a forcing chain. Forcing chains have been a problem and I guess I will have to work on it although I though I had it down "pat".
Gee

Posts: 50
Joined: 18 March 2007

To me, forcing chains are last hope.

This is an easy puzzle.
Code: Select all
`Easy stuff to an xy wing.  Pretty much done..---------------.---------------.---------------.|*25   259  4   | 3    8    79  | 1    27   6   || 1    3   *28  | 6    5    79  | 4    27   89  || 68   69   7   | 4    2    1   | 5    89   3   |:---------------+---------------+---------------:|*58   57   3   | 79   1    6   | 2    89   4   || 4    27   2-8 | 79   3    5   | 6    1    89  || 9    1    6   | 8    4    2   | 7    3    5   |:---------------+---------------+---------------:| 3    8    5   | 2    7    4   | 9    6    1   || 26   26   1   | 5    9    8   | 3    4    7   || 7    4    9   | 1    6    3   | 8    5    2   |'---------------'---------------'---------------'If you prefer bugs,  use them!.---------------.---------------.---------------.| 25   59-2 4   | 3    8    79  | 1    27   6   || 1    3    28  | 6    5    79  | 4    27   89  || 68   69   7   | 4    2    1   | 5    89   3   |:---------------+---------------+---------------:| 58   57   3   | 79   1    6   | 2    89   4   || 4    27   28  | 79   3    5   | 6    1    89  || 9    1    6   | 8    4    2   | 7    3    5   |:---------------+---------------+---------------:| 3    8    5   | 2    7    4   | 9    6    1   || 26   26   1   | 5    9    8   | 3    4    7   || 7    4    9   | 1    6    3   | 8    5    2   |'---------------'---------------'---------------'`
wintder

Posts: 297
Joined: 24 April 2007

Hi Winter....Yeah, forcing chain have been the hardest of the Sudoku solving techniques for me to learn. In fact, I am still at it. Thanks for your reply.

Glenn
Gee

Posts: 50
Joined: 18 March 2007