Tue, 28 Jul 2020 13:48:59 +0200
adds more tests
1 _ _ _ 1 9 _ _ _ 8
2 1 _ _ 2 _ 7 9 6 _
3 6 9 _ _ _ 4 _ _ _
4 _ _ _ _ _ _ 1 _ _
5 _ 5 _ 6 _ 9 _ 7 _
6 _ _ 3 _ _ _ _ _ _
7 _ _ _ 9 _ _ _ 8 1
8 _ 1 6 7 _ 8 _ _ 3
9 9 _ _ _ 1 2 _ _ _