Diagonal Sudoku (X-Sudoku)

Diagonal Sudoku (X-Sudoku) rules

1. 1
   Rule 1

   The classic row, column, and 3x3 box rules apply as usual.

2. 2
   Rule 2

   The diagonal running from top-left to bottom-right contains 1-9 once.

3. 3
   Rule 3

   The same rule applies to the diagonal from top-right to bottom-left.

4. 4
   Rule 4

   The lightly shaded cells on the grid are the diagonal cells.