Sudoku Players' Forum (clone)

It shows up all the time if one or more of the a's or b's is fixed as a clue. Otherwise it could be permuted to an alternate solution making the sudoku invalid.

Another configuration is:

Code: Select all

+-------+-------+-------+
| . . . | . b . | a . . |
| . . a | . . . | b . . |
| . . b | . a . | . . . |
+-------+-------+-------+


I've been watching for these configurations to show up where the uniqueness rules could be applied but since the basic form would require 5 of the 6 cells to reduce down to the same naked pair it's not going to be very common.

I've almost seen it a few times, but I guess it's probably very unlikely to ever actually occur for some statistical reason. It's certainly a theoretical possibility though.