PlaySudoku.us
Hard · Puzzle #487
9
3
5
6
8
7
4
5
6
5
9
4
6
2
2
8
7
9
4
1
7
9
7
3
8
9
1
2
Set theory provides the formal foundation for Sudoku's rules: each digit must appear exactly once per set.
Set theory provides the formal foundation for Sudoku's rules: each digit must appear exactly once per set.
"The important achievement of Apollo was demonstrating that humanity is not forever chained to this planet." — Neil Armstrong
"The important achievement of Apollo was demonstrating that humanity is not forever chained to this planet." — Neil Armstrong