The New Sudoku Players' Forum

[kurbads]

I had a feeling that the 1 in right top corner was the one. But I kept an eye on it and it did turn out to be 1.



...|...|2.5
.57|...|.36
..6|83.|.1.
---+---+---
...|.68|.9.
...|4.1|...
.4.|97.|...
---+---+---
.2.|.46|7..
61.|...|34.
7.4|...|...

[Leren]

Code: Select all

*-------------------------------------*
| 4   3 1   | 6  9  7   | 2    8  5   |
| 8   5 7   | 2  1  4   | 9    3  6   |
| 2   9 6   | 8  3  5   | 4    1  7   |
|-----------+-----------+-------------|
|b135 7 2   | 35 6  8   |a1-5  9  4   |
| 359 6 389 | 4  25 1   | 58   7  23  |
|c135 4 38  | 9  7  23  |d1568 26 123 |
|-----------+-----------+-------------|
| 39  2 39  | 1  4  6   | 7    5  8   |
| 6   1 5   | 7  8  29  | 3    4  29  |
| 7   8 4   | 35 25 239 | 16   26 129 |
*-------------------------------------*

Feelings are nice but proofs are better, at least on this forum .

There is a Hidden UR on 15 in the cells abcd. In words, if a is 5, it is not 1, so in Row 4, b must be 1 (and not 5). Then in Column 1, since b is not 5, c must be 5. In Column 7 since a is not 1, d must be 1.

a = 5, b = 1, c = 5, d = 1 is a Deadly Pattern, and can't be True in a puzzle with 1 solution, so a is not 5.

Perhaps an easier move is a Skyscraper on 2 in cells abcd below.

Code: Select all

*-----------------------------------------*
| 4   3 1   | 6   9    7   | 2    8   5   |
| 8   5 7   | 2   1    4   | 9    3   6   |
| 2   9 6   | 8   3    5   | 4    1   7   |
|-----------+--------------+--------------|
| 135 7 2   | 35  6    8   | 15   9   4   |
| 359 6 389 | 4  a25   1   | 58   7  b23  |
| 135 4 38  | 9   7    3-2 | 1568 26  123 |
|-----------+--------------+--------------|
| 39  2 39  | 1   4    6   | 7    5   8   |
| 6   1 5   | 7   8   d29  | 3    4  c29  |
| 7   8 4   | 35  5-2  239 | 16   26  129 |
*-----------------------------------------*

Hopefully it is easy to see that one of a or d must be 2, so you can remove two 2's as marked.

Leren