Normal sudoku rules apply. Cells a king's move apart are not allowed to contain identical digits. The digit in the central cell of each box is less than or equal to the box number. Boxes are numbered in normal reading order. Each horizontal 3x1 region that is completely contained in a single box sums to the same value. Each vertical 1x3 region that is completely contained in a single box sums to the same value. The digit in the top-left cell and the digit in the bottom-right cell of the grid sum to 3.