data/paper_stepwise/trace_solution.txt

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