The New Sudoku Players' Forum

[EnderGT]

The original:

Code: Select all

6..|...|7..
2..|..8|...
..3|9..|..5
---+---+---
1..|...|4..
.8.|3.2|.9.
..5|...|..6
---+---+---
4..|..1|2..
...|7..|..3
..9|...|..7


At the stuck state:

Code: Select all

6     9     14    |  24    5     3     |  7     128   28
2     5     17    |  16    167   8     |  9     3     4
8     147   3     |  9     127   47    |  16    126   5
------------------+--------------------+------------------
1     3     26    |  568   6789  569   |  4     278   28
7     8     46    |  3     46    2     |  5     9     1
9     24    5     |  18    178   47    |  3     278   6
------------------+--------------------+------------------
4     67    78    |  568   3     1     |  2     56    9
5     126   128   |  7     4689  69    |  168   146   3
3     16    9     |  24    2468  56    |  168   1456  7


The built-in solver (not my implementation) suggests a Forcing Chain as the next step, specifically [R1C3] -4- [R5C3] -6- [R4C3] -2- [R4C9] -8- [R1C9] -2- [R1C4] -4- [R1C3].

To me, this feels like making a guess, and so I'm not happy with using it, but I'm having trouble locating any other way to progress in this puzzle. Any suggestions?

[hobiwan]

Lot's of chains and some ALS, for example:
Almost Locked Set XZ-Rule: A=[r6c4568] - {12478}, B=[r2c45],[r3c56] - {12467}, X=4, Z=2 => [r3c8]<>2

[EnderGT]

Lot's of chains and some ALS, for example:
Almost Locked Set XZ-Rule: A=[r6c4568] - {12478}, B=[r2c45],[r3c56] - {12467}, X=4, Z=2 => [r3c8]<>2

Yeah, I ended up finding an XY-Chain that did the same thing the suggested Forcing Chain did. Specifically, R1C4 and R5C3 are linked to remove the 4 from R1C3.