The New Sudoku Players' Forum

[rubylips]

The chain logic doesn't hold because there are many 3s in Columns 6 and 9.

I can't believe I wrote that sentence. Of course, I meant Rows 5 and 8.

[tso]

If these are the only spots in ROW 2 and 3 where a 1 can go ...

Code: Select all

 x x x | . . . | x x x
 1 a a | a a a | a 1 a
 a a 1 | a a a | 1 a a 
-------+-------+-------
 . . . | . . . | . . .
 . . . | . . . | . . .
 . . . | . . . | . . .
-------+-------+-------
 . . . | . . . | . . .
 . . . | . . . | . . .
 . . . | . . . | . . .

If these are the only spots in BOX 1 and 3 where a 1 can go ...

Code: Select all

 a a a | . . . | a a a
 1 a a | x x x | a 1 a
 a a 1 | x x x | 1 a a
-------+-------+-------
 . . . | . . . | . . .
 . . . | . . . | . . .
 . . . | . . . | . . .
-------+-------+-------
 . . . | . . . | . . .
 . . . | . . . | . . .
 . . . | . . . | . . .

The same eliminations may be made even when several 1s exist in both rows 2 and 3 of both boxes 1 and 3.

Yes, I've over-reached there.
These are actually examples of "locked candidates", a much simpler tactic.
In the both diagrams, one of r1c456 must be 1. This excludes 1's from the rest of the row in the first diagram and the rest of the box in the second.