Nice move

Para · Post by **Para** » Tue Jan 02, 2007 11:26 am

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

Take this puzzle.
After the initial steps you come up with the situation below.

Code: Select all

.------------------.------------------.------------------.
| 128   28    5    | 147   347   1237 | 78    6     9    |
| 7     3     4    | 8     6     9    | 12    25A   125  |
| 6     9     128  | 157   57    127  | 78    4     3    |
&#58;------------------+------------------+------------------&#58;
| 238   4     2378 | 6     137   5    | 12B   9     1278B|
| 5     78    3789 | 2     1379  4    | 6     378   178B |
| 239   1     6    | 79    8     37   | 5     -237  4    |
&#58;------------------+------------------+------------------&#58;
| 389   5     3789 | 479   2     6    | 49    1     78AB |
| 4     6     12789| 1579  579   178  | 3     2578A 25-7-8|
| 1289  278   12789| 3     457   178  | 49    2578A 6    |
'------------------'------------------'------------------'

There's 2 similar ways to make the same eliminations.
Take the 4 squares marked with an A. The squares in R89C8 can't both be 7 or 8 cause this would interfere with R7C9 and can't be both 2 or 5 because this would interfere with R2C8. So R89C8 contains either a 2 or a 5 and either a 7 or an 8. This creates a "naked pair" 7-8 in box 9 with R7C9 which eliminates 7 and 8 from the remaining squares of box 9. It also creates a "naked pair" 2-5 with R2C8 for column 8 which eliminates 2 and 5 from the remaining squares in column 8.
So we can eliminate the 2 from R6C8 and the 7 and 8 from R8C9.

The same goes for the squares marked with B for 1 and 2 in box 6 and 7 and 8 in column 9. This makes the same eliminations.

Para