Starting board:
- 4 - 1 2 - 5 - 7
- - - - - 4 1 - -
6 1 2 - 3 - - 4 -
- 2 - - 6 - - - 3
9 - 3 - - - - - -
- - 6 - - - - - -
2 7 - - - - 4 5 1
- 6 - - - 1 - 7 -
- - 1 - - 2 - - -
Solution:
8 4 9 1 2 6 5 3 7
7 3 5 9 8 4 1 6 2
6 1 2 5 3 7 9 4 8
1 2 7 4 6 5 8 9 3
9 5 3 2 7 8 6 1 4
4 8 6 3 1 9 7 2 5
2 7 8 6 9 3 4 5 1
3 6 4 8 5 1 2 7 9
5 9 1 7 4 2 3 8 6
Some info on the solution, gleaned from the solver script:
Solved cells at each "natural" level: 1:0, 2:0, 3:0, 4:0
Total progress made by natural solver: 0.
(So, there's a solution all right, but you can't get there from here.)
Guess steps: 4
Backtrack steps: 2
Max depth: 2
Final depth: 2
(That means the solver was 2 levels deep in guessing when it got the
answer. It also means it guessed wrong twice and consequently had to
back up. Backing up, when solving board by hand, is, to say the
least, tedious.)
Solver level: 5
Raw rating: 7.94
Stars: 4
But note that the 'stars' rating assigned by my solver, while pretty
close to the Conceptis rating for level 2 and 3 boards, is typically
too low for high-solver-level boards. You never see boards like this
in the newspapers so I don't have much to calibrate it against.
Really, a charming puzzle.