Revision control
++ 0, 0, 0, 2, 6, 0, 7, 0, 1
++ 6, 8, 0, 0, 7, 0, 0, 9, 0
++ 1, 9, 0, 0, 0, 4, 5, 0, 0
++ 8, 2, 0, 1, 0, 0, 0, 4, 0
++ 0, 0, 4, 6, 0, 2, 9, 0, 0
++ 0, 5, 0, 0, 0, 3, 0, 2, 8
++ 0, 0, 9, 3, 0, 0, 0, 7, 4
++ 0, 4, 0, 0, 5, 0, 0, 3, 6
++ 7, 0, 3, 0, 1, 8, 0, 0, 0