Normal sudoku rules apply.
Every 1, 2, and 3 has an anti-knight's move constraint.
Every 4, 5, and 6 has an anti-king's move constraint.
Every 7, 8, and 9 has an anti-bishop's move constraint.
Every Knight is either a 1, 2, or 3.
Every King is either a 4, 5, or 6.
Every Bishop is either a 7, 8, or 9.