The objective is to fill the grid with numbers from 1 to 9 in a way that the following conditions are met: Each row, column, and nonet contains each number exactly once.The sum of all numbers in a cage must match the small number printed in its corner.No number appears more than once in a cage. (This is the standard rule for killer sudokus, and implies that no cage can include more than 9 cells.)In 'Killer X', an additional rule is that each of the long diagonals contains each number once.