the rules of 8x8 Sudoku:
The puzzle is played on an 8x8 grid, instead of a 9x9 grid.
There are 8 numbers to choose from (1, 2, 3, 4, 5, 6, 7, and 8).
Each row, column, and 4x4 block must contain each of the numbers 1, 2, 3, 4, 5, 6, 7, and 8 exactly once.