- Code: Select all
XY+ XY+ XY+ | XY / / | / / /
XY ** ** | . . . | . . .
** ** ** | . . . | . . .
------------+-----------+----------
. . . | . . . | . . .
. . . | . . . | . . .
. . . | . . . | . . .
------------+-----------+----------
. . . | . . . | . . .
. . . | . . . | . . .
. . . | . . . | . . .
Row 1 has a bivalue cell with candidates XY, and all other candidates for X & Y are located in the intersection with box 1.
Box 1 also has a bivalue cell with candidates XY. Because the intersection must contain an X or an Y, we can eliminate candidates for X & Y from the remaining cells in box 1.
It should be possible to generalize this to larger ALS sizes in either of the intersecting sectors.
Here is a real-life example. It is a Sudoku-X (with diagonal constraints), but the move does not use the diagonals. It is the only example I have, so far.
Original puzzle:
- Code: Select all
. . .|. . .|. . .
3 . .|5 . 7|. . 2
. . .|. . .|. . .
-----+-----+-----
4 6 .|2 . 9|. 7 8
. 9 .|1 . 8|. 4 .
1 2 .|7 . 5|. 6 3
-----+-----+-----
. . .|. . .|. . .
8 . .|9 . 4|. . 7
. . .|. . .|. . .
Here is the point where this technique can be used, bypassing several other steps:
- Code: Select all
.------------------.------------------.------------------.
| 9 1458 1246 | 346 18 236 | 7 135 14 |
| 3 148 146 | 5 9 7 | 46 18 2 |
| 256 1458 7 | 346 18 236 | 3458 1359 69 |
:------------------+------------------+------------------:
| 4 6 5 | 2 3 9 | 1 7 8 |
| 7 9 3 | 1 6 8 | 2 4 5 |
| 1 2 8 | 7 4 5 | 9 6 3 |
:------------------+------------------+------------------:
|#56 -13457 124 | 368 57 136 | 348 12589 69 |
| 8 %135 %16 | 9 2 4 |#56 13 7 |
|-25 -13457 9 | 368 57 136 | 4568 1258 14 |
'------------------'------------------'------------------'
I assume this is a rare move, as nobody has mentioned it before, but the generalized version may be more frequent, yet undetected.
Should I be embarrassed for not spotting a simple alternative?
Ruud