The New Sudoku Players' Forum

[enxio27]

I can't see any further moves with this puzzle. I was thinking it was invalid (multiple solutions), but Richard Piarina's SudokuSolver solved it. However, the next move it gives me is a naked double at r8c1/r5c2, which is obvious to me, but I don't see that it eliminates any candidates. Any ideas?

[JC Van Hay]

[6r8c1=6r5c2]-6r8c2 OR [4r8c1=4r5c2]-4r2c1 solves the puzzle.

[enxio27]

[6r8c1=6r5c2]-6r8c2 OR [4r8c1=4r5c2]-4r2c1 solves the puzzle.

Why? I'm missing the logic here. Why is the 6 ruled out in r8c2 and the 4 ruled out in r2c1?

[JasonLion]

The sixes in r8c1 and r5c2 are strong linked, that is to say that one or the other must be true. Since r8c2 "sees" both of those cell's it can't contain a six.

[enxio27]

The sixes in r8c1 and r5c2 are strong linked, that is to say that one or the other must be true. Since r8c2 "sees" both of those cells it can't contain a six.

Oh, I see that now. Thanks! For some reason, I can see those with standard vanilla 9x9 (3x3) puzzles, but they seem to escape me with jigsaw puzzles.